Transmission Failure B2 Piston?

My transmission in my 84 300D failed a few weeks ago. It will not go in any forward gear but works fine in reverse. I'm led to believe this is a common problem caused by the B2 piston failure in older transmissions and the MB has a revised part out for 10 years or so.
An article I found on the net describing the fix indicated that it would not require a complete transmission rebuild and that on 126 cars (SD) it could be done with the transmission in the car. It implied that the close quarters in others made an "in car" repair very difficult.
Has anyone had experiance with this repair and is it possible in my 123 car (84 300D) to do it without removing the transmission?
Thanks,

Bruce