Vibration in engine/trans
 

I recently replaced the automatic transmission in my 81 300D. At that time the car contracted a vibration (more noticeable as engine speed increases). Thinking I had a defective converter, I than replaced that. The vibration persisted. When I replaced the trans I also had the flexplate/flywheel off. Is it possible that the flexplate to crank bolts were improperly torqued? Also, the flexplate has 12 evenly spaced bolts. Does it have to be indexed when installed onto the crank? By the way, after the trans install, the engine developed a slight oil leak, perhaps at the rear main seal.

Flexplates do crack, but not from improper bolt torque, but rather from the housing the tranny connects to coming loose. IF you look closely, the tranny doesn't connect straight to the engine, but rather to an adapter that is connected to the engine. I have had to index these in the past.