At least the pan can be taken off and dealt with on the bench or in a shop. I hate playing blacksmith when parts are still on the car!
For the torque converter try a different 5mm allen wrench. Yours may be worn with a rounded tip. Grind some of the tip down to get sharp corners. Clean the bolt hole of any crud that can prevent total engagement.
I believe the aluminum washer is the problem. It galls readily. I'll have to remember to replace it with copper next time.
95 E320 Cabriolet, 131K