I wonder if you experts are still out there so many years since.
I have a 79 TD
The classic B2 thing happened to me -- no forward gears but reverse works
I have the same piston pictured and described above, with the metal seal ring.
So far I have everything out except the piston, which doesn't seem to be able to move.
Do you think the problem lies in its being stuck?
Or does the metal ring make it hard to move?
How would you advise me to get it out?

And for my sins, I damaged the yellow plastic hub cover when fiddling with the circlip. Would anyone know where I could get another like it?
Thanks
Dirk