He may be talking about this article........
Pretty much runs down the models that are allegedly affected, but only lists the tranny #'s as "specific numbers within the 722.XXX category". ( DOH! )
I had wondered about the frequency of failure with the B2 piston as well, being an owner of a W126.
The article also states...
"The W126 chassis (S body) is the only affected chassis in the Mercedes-Benz line that will permit easy removal/replacement of the B2 piston with the transmission remaining in the vehicle. "
I guess that's a good thing(??arrgh??) in my case. Thankfully, my car exhibits none of the symptoms he references in the article.......( knock on wood!