Go to your local transmission parts house and buy an ATSG manual. Someone posted here that the manual wasn't very good for these transmissions but it is probably good enough to make you change your mind about cracking the transmission open.

A buddy of mine who rebuilt transmissions for many years never said a good word about a MB transmission.

If you have seen wet multi-plate clutches like in a motorcycle, the insides of an automatic wouldn't look too strange to you. Planetary gears and clutches applied with hydraulics, that is about it.