My apologies--my diagnostics and attempts to understand this problem have so far been based on a brief tour under the transmission cover last weekend, the suggestions kindly offered by the readers of this board, and a too-cursory glance at the diagram posted by JohnMc. In my haste to feel relieved I looked at the diagram backwards (in a small browser window, could not see shift lever telling me which way was front!) and blamed the wrong dog. Saturday I will have time to properly break down the top end of the trans and learn what I am talking about...thanks for bearing with me.

The shifter is well and truly locked up--that is, there is some fore-and-aft play within the third gear area, but it ain't moving past a wiggle.

When replacing the seals in this unit I removed the OD section completely--it's very likely that the mainshaft could have moved while I was dis- or re-attaching it.

I remain hopeful until further notice from the innards of a certain M41.

All best,
Nathan