Hmmm, this gets more interesting. I bought the '91 300SE brand new, and the only time it has had any work was when I personally took the trans off last year to change the engine rear main seal. I had not been able to fine the torque converter drain earlier (there is the access port and plug in the shield) so while I had the trans out I REALLY looked for the drain plug. It just does not exists, and i can guarantee this is a factory tranny and converter, unless it got changed in the first 8 miles.
Oh well, I just drain out the 2-3 quarts occasionally and replace them, so far zero tranny issues in 140k miles.