I have not had the boat in the water in a  few months and when I got her in on Saturday, I could hear a dribble. It was steady like it was coming thought a coffee stirrer straw. Not a lot of volume but it was steady enough to not be a mere drip. I could not see exactly where it was coming in  from but it was coming in. My bilge pump could surely take care of it but I decided to trailer her back up and go home instead of risking it.  I am thinking shift cable because the previous owner had that  done not long before I adopted it. but not 100% sure. Either way I figure if I am pulling the drive, may as well get em all regardless.

I figure it best just to change all the seals and wondered how hard it might be and what it would cost me? Its a Volvo Penta SX on a Penta 5.0

SX drives don't use a shift cable bellow. The cable feeds into a hardwall rubber hose through the transom assembly. The hose protrudes in and up behind the engine and is higher than the water line so it doesn't take on water.
I have seen the hoses go bad and the hose fitting in the transom assembly rot out.
My suggestion is to take it back to the lake with a small mirror and a very bright flashlight and find the leak. Tearing it all down and "re-rubbering" only to find the transom seal is leaking will be a waste.

What year and engine? I know you said 5.0, but Ford or GM? Make of boat?

2001 Volvo Penta 5.0 GL (carbed)

Glastron GS 249

Will try to dunk it in this Saturday and do like you said.

I usually start by holding the mirror down below the harmonic balancer and shine the light into the mirror. This will reflect the light and your view under the oil pan to the very back/bottom of the bilge just above the drain plug.
I can usually at least narrow it down to which side I'm going to have to crawl into to pinpoint the leak.
ETA - If it is the shift cable hose, don't pay Volvo's ridiculous price for it. Go to NAPA and have them make you a partial hydraulic hose. Make sure the fitting is stainless.

When out of the water can the hull be slowly filled with water until water leaks out?  Obviously without causing any damage.

This may work also depending on where the leak is. Don't fill the boat to the point where the starter is submerged.
There is also a possibility the boat (on a trailer) will tip backwards if there isn't enough tongue weight on the trailer. Place a jack under the rear of the trailer to prevent tipping.

Found a slit in the UJoint bellows (Top bellows)

Looks like I have a fun project ahead of me.

Meh. That isn't too bad of a job. Be sure to replace the gimbal bearing while you're in there. Was there any oil inside the bellow?

Not much. I peeked at it with a light and the u joints looked ok at least.

I will order a kit but some said stay away from Sierras bellows.

They passed pre purchase inspection , didnt leak until now and look pretty new. I wonder what tore it.

I am guessing it went sometime I last had it out. How much damage am I probably looking at? I didn't run it hard much, mostly 2k rpm. WOT for 10 minutes tops.

Sierra bellows are, well, not as good as the factory ones. Grease the living crap out of the u-joints to force any water out of them if you don't replace them. Oil in the bellows means the driveshaft seal where it enters the drive may be leaking. Look closely at the seal under the yoke where it meets the housing. It may also be grease that has thinned out over time and look like oil.
Be mindful of where the clamps are oriented. Placing the clamp adjuster in the wrong spot could snag the bellow and you're back to square one. Check against factory placing, not what may be on there now.
Most of the time when we get submerged gimbals/u-joints we replace them all. Seems every one in which we replace the bellows and gimbal bearing but not u-joints (per customer) we see it back some months down the road with vibrations due to bad/rusted u-joints.

Bellows and gimble bearing done. No oil in it , it was old grease. I borrowed and alignment tool and to my surprise and relief, it was good.

I am building a sled lift type thing for next time. Man what a bitch it was getting back on due to the weight lol.

Good job! Alignments aren't that difficult. The only thing you can adjust are the front motor mounts. The rear mounts are fixed with no adjustment.
I have re-installed a lot of drives with no lift. It's a pain. Try wrestling a Bravo 3 or Volvo DP onto a transom. We do have a dedicated drive "jack" but it's sometimes being used when I need it and I don't like waiting around to finish a job.