I don't know what the reman's predone cost, but (it's been a few years) my dad had his diesel C6 done and installed for $400, might be worth asking around to see what it cost. As for the leak, how certain are you it is coming from betyween the motor and converter, or is it just draining out the access cover? If so, i would lay money down on a failed front seal. If it is slipping, be certain that the fluid level is right, if it is low, get it up to be sure. If it behaves for a while, then slips again, recheck the fluid, as the front seal will get rid of fluid fast. I guarantee it will act failed if it gets low on fluid. The nice thing is, if you don't run it too much, it can be saved by simply dropping the trans and replacing the seal. But if the trans has been damaged, I would price check a rebuild, because the parts are cheap, it's more the cost of labor. Another thought, if you really want to be sure, is drop the trans pan to see what it looks like there. If it has a lot of sediment, that is clutch material. Some is normal, a lot is not, if it looks like mud on the bottom of the pan it's so thick, then the clutches are pretty hurt. Chunks are not good.