98 Buick Park Avenue, Mechanic called and said the car was running like a charm. He also said that there is a whining noise and a leak coming from the tranny. This vehicle went in because the motor was gone, it ran hot at first and would not start. Had a mechanic look at it and he saw that it had to much oil in it and a coil was bad. Drained the oil and repalced the coil and the car started. It smoked alot and he said it was oil in the catalytic converter. It sat up for a while before going to get the converter changed, when I took it to have the changed out, it wouldn't start or turnover period, even trying to turn the crank by hand. There wasn't a problem with the tranny prior to it going into the shop to have the motor replaced. Could the mechanic have installed something wrong? Or is this a condition that could have been caused because the car was sitting up for a while? Once again The tranny never leaked or had any problems.

When an engine overheats, the transmission temperature will increase as well.During an overheat,
heat from the engine is trapped inside the bellhousing and, the transmission cooler lines that run through the radiator where the fluid is being heated instead of cooled. these conditions combined will quickly deteriorate the trans fluid to the point that is no longer can do it's job. If the leak is minor and the trans is shifting properly, I would change the trans fluid and filter and add a good additive such as the one made by lucas. If the leak is not very small, I'd have the trans rebuilt before using the car.
The part you wrote about not being able to turn the engine by hand. Is that after the engine was changed? If so you don't want that engine (may be leaking coolant into the cylinders and causing "hydro-lock") In that case the smoke is not from the converter, but coolant steaming in the exhaust system. Overfilling the oil in the crancase will not cause a no start though it can damage seals and enbine bearings but that takes time. I see a problem here. Either you have the order of events confused or I read this wrong, or your mechanic should be doing some other kind of work (making hamburgers?)