ps2cho,
My car has had very little reverse for six months now and I have learned to deal with it. My 400E had the very same problem and when the dealer pulled it out, they found that only the B3 was worn--the forward discs and bands were perfect. In fact you could still see the Mercedes logo on the discs after over 200,000 miles. The tech recommended just doing the B3. It was stil $3,600 and I probably overpaid for it (that's to be expected at a dealer).
Now, when I take my existing car to an indy to have the transmission done, I am thinking of only having them do the B3 and seals, but for my own information, what seals are you referring to? Can you get to all that will likely need replaced without going too deep into the transmission? Approximately how much time would be saved by just doing the B3?
I want to compliment you for taking the initiative of diving head first into your 722.3xx without hesitation and getting it done. That's a job many of use here wouldn't dare tackle.