Make sure you use only MB trans fluid. You are just asking for trouble otherwise. It's a bit spendy, but worth it in the long run. I've seen early 722.6's that have broken snap rings inside the case and let the planetary set go loose causing catostrophic failure. There is also one common culprit spring in the valve body that will cause a hard third gear shift and will delay engagement of reverse. I agree that this is probably something to have the professionals look into, especially before you go and spend a decent chunk on expensive MB synth trans fluid which may end up getting partially or fully drained during necessary repairs anyways. The sooner you catch these things, the better.