Decided I had enough brass backing up and it was time for some SS Tumbling.  Haven't used it in a couple of years now.  Just been sitting in my garage.  Anyway got my first load loaded and turned on last night.  I checked it every once in a while to make sure all was well.  When I went to turn it off at the 4 hour mark I noticed the barrel was not spinning.  So took a quick look and the rollers underneath the barrel were spinning but the barrel was idle.   So it appeared the rubber rollers might have been a little dried out.   So I took some silicon and rubbed on the rubber.   Seemed to help somewhat but mostly minimal effect.   It was late so I just turned things off and went to bed.

This morning attempted again but this time it also appeared the drive belt from the motor was just spinning on the pulley and not even driving the rollers underneath the barrel.   I opened up the barrel and it appeared the brass from last night seemed to have been cleaned pretty well.  Cleaned all that brass up and prepped another load.  Same thing.   Drive belt from motor just spins on the pulley.  Thought well maybe it's too heavy.  Model B is 16 lbs rated.   So I removed a couple of handfuls of the brass and tried again.  Same thing.

Anyone ever had to replace parts from a Model B tumbler?  It would be nice if there was an adjustment for the drive belt tension.  Either way I see them on Amazon.

I replaced the belt on mine because it started cracking.

I replaced the shafts, bearings, and rollers too.

Make sure to oil the white bearings and put a few drops in the holes on the motor housing.

Dryflash gave me that tip.  It helps.

I have had to replace the drive belt about 5 years ago, and also bought some new rollers as the old ones were pretty worn.  I mounted some skateboard tape on the drum too, and now it works much better.  The new rollers and drive belt have been working for hundreds of hours so far.

You would be happier with the Frankford Arsenal tumbler.

I got tired of the belt slipping, lubing, etc of a similar tumbler I used to use and am quite happy with the Frankford.

I usually tumble for 2 hours.

My FART leaks so much it is unusable, whereas my Thumler's has never leaked.  I would really like the FA tumbler if not for the leaking.

Speaking of which, I need to call FA (again) to see if they will replace the drum

I'm guessing(hoping) the issue with mine is basically being stored in an unconditioned garage with it's hot and cold extremes.  Perhaps not so favorable to the pliable rubbery parts.   Belts on order.   I like the idea of the bracket.  Pretty sure I've read through your topic several years back.  Just been out of the game for a few years now.

I make sure the seal is wet before putting lid on.  No leaks. Hopefully you are putting the seal on the correct side of the lid insert.  

I've tried wetting the gaskets before putting them on, drying them before putting them on, warming them in the sun (per FA's customer service rep) before putting them on, hand tightening, tightening with a strap wrench, everything I can think of and it still leaks out of both ends.  I even tried teflon taping the threads.

Mine came with the gaskets slipped over the inserts (gasket between drum and insert).  That's how I run it and it leaks.  The rubber inside the drum is hand trimmed.  I'm thinking it might have been trimmed back too far on my drum.

Clean the rubber rollers with alcohol, not silicone. Silicone will make the slippery, not the direction you're trying to go.
The belt slipping is often caused by oil on the motor pulley. Try cleaning the belt with alcohol, and use brake cleaner on the pulleys. If you over-oil the motor bearings, the excess oil from the front bearing will often travel down the shaft to the pulley.

In a pinch, the rubber rollers can be replaced with fuel line hose but it won't last as long as the factory pieces, but fuel line is a lot easier to get locally.

OP,
     I have been using the same Model B since the '70s and the original motor still runs fine. Just had to replace the rubber rollers/lid gasket/drive belt as they were no longer serviceable. The drum would not turn because the rubber rollers had hardened & would just slip against the drum instead of gripping it. I tried cleaning and roughening the rubber drive rollers but no luck. Roller parts or complete shafts, etc. are available online: https://rocktumbler.com/tumbler-parts.shtml. Mine is back working like a champ again and the drum does not leak. HTH

Yep I found all the spare parts on that site.   I think that is actually where I originally bought mine from.

One last detail that might be of use. The old Model B drum was painted red on the outside. But the older drums were left bare metal and not painted at all on the inside. With wet tumbling, the inside of the drum corroded very badly due to the high moisture. So I simply wire brushed the oxidation/corrosion/rust off the interior of the drum and painted it the same fire-engine red as the exterior. And voila, no more rust! .02

And I just covered it in my post. It is important if you want the drum to last. My drum is now 44 years old give or take. It even survived the flooding in Kingwood, TX due to Cat 4 Hurricane Harvey in 2017. All I had to do was repaint the drum, flush the original motor out with flesh water, and let it dry which is flat amazing!

Yep and this is something I still need to take care of.   It's been sitting long enough I should have already accomplished this simple task.   I am noticing the back side of the cover plate(that rests up against the gasket) is showing rust spots through the paint.  Once I get it working correctly again I will add the inside paint.  Afraid to even look under the rubber insert at this point.   lol

Maybe I should oil my Thumbler's tumbler, but I fear that doing so might spoil it and it would finally decide it could quit working.  I run the thing for hours and hours whenever I use it.  I use either stainless pins, or crushed walnut shells.

For those who want to save money, I buy crushed walnut shells in a 50 pound sack from industrial safety supply houses at a fraction of what gun shops sell it for.  IIRC the last 50 pounder I bought about 12 years ago cost me around $20-30.   They also sell corn cob media.  Industrial uses are to soak up oil or solvents or other liquids, provide traction to slippery floors in machine shops, etc.

New drive belts came in today.   Oh man....I could tell right away how stretched the original belt was when installing a new one.   New ones much snugger.   Barrel spinning like a banshee now.

As an added bonus, Thumler is US made.