Got 50K on my Jeep (bought used) and I am just thinking about putting a good synthetic oil in the TC and the diffs. What are your guys experiences on this and any possible leaks (none now) this late in the game. Its cold up here in No. Minn., and with short trips in town the synthetic might be nice.

Changing to synthetic oil CANNOT start a leak.  If you have an existing leak it will most likely make it worse.  It does not matter how many miles you have on anything, gears, engine, whatever changing to synthetic will not hurt.  Why you want to do it, and if it is justified is up to you.  But as far as creating a leak when changing to synthetic is non existent.  

When synthetic oils first came out it got a bad reputation for creating oil leaks, so to speak. The truth was that petroleum based motor oils would deposit sludge over time and actually plugged some leaks in much the same way radiator leak sealers work. The change over to synthetic oils on high mileage vehicles would act like a detergent, clean and unplug any pre "existing" leaks which was initially, and still to some degree, blamed on synthetics.

So as already stated, synthetic oil cannot start leaks, but it can expose them or make them worse.

I run synthetic's in my 61 MB and my Motorcycle.. No leaks what so ever.  as already stated, the change to syth. should not cause any problems (other than $$$)  [:)]

Synthetic is the way to go...

I switched over to synthetic oil in my drag car a few years ago...

I used 5W-50 in the motor, and 85W-90 in the rearend...

I noticed a drop in ET, and a gain in MPH...

The gears in the rearend were MUCH cooler after a run with the synthetic oil...
Bearings in the engine looked brand new after a whole season of Nitrous assisted 160MPH passes down the track too...

I'm a believer in the stuff...
Timeslips showed definate results...

The best synth oil I found after a long search is Redline. I used the motor and gear oils. Worked great. Quieted down the gear noise quite a bit. Also tried the Redline Water Wetter product. Supposed to help water conduct heat better while avoiding rust. I liked it.

And no, I don't work for them. :')

When I bought my truck in the late 80's, the 5-speed tranny was stiff as hell. So, after 1,000 miles I replaced the tranny oil and ran that for another 500 miles. Still stiff as hell. I had to almost jam the thing into gear. So, I replaced the tranny oil again but this time I used Redline synthetic. The difference was absolutely amazing. It shifted much smoother -- the gear shift just slid into gear, where before I had to almost force it in. Granted, it was a new truck so perhaps the tranny was tight, but the difference was like night and day.

As far as their motor oil, I have heard nothing but good about Redline motor oils.

This was actually a topic of discussian between me and the maintenance instructer of a class i was attending. We ended up calling Mobile Oil and they said synthetic oil will cause leaks only when they've been added to an engine thats been poorly maintained and usually past seventy or eighty thousand miles. Seals which have been damaged by acid and oxidized particles tend to "wash out" under the strong detergent action of synthetic oils. So if your seals are in pretty good shape you've got nothin to worry about.

I don't know about engines that have had wear & tear on them, but using anything but Mobil-1 synthetic will void the warranty on my Porsche.  I tend to think the crazy Germans know what they're talking about, but that's just me.  I've converted my other high-mileage vehicles to Mobil-1 Synthetic and haven't noticed problems.  YMMV.  Sniperm88's suggestion does make sense to me.

    Black Fox