I would be checking the salvage yards pricing for an MB transmission. Or have vstech strap that $50 trans. to a pallet and have it shipped freight collect.

I would not pour another $4,500 in a 26 year old, rusting MB with 311K miles on it. Once I saw the rust, (the kind you described) the relationship would be over. BTDT.

The car in question isn't worth $2,500, IMO, much less $4,500 with rust.