yah sorry, I still intend to do a full write-up, just finishing another quarter of engineering school...
swissfrank...you were 100% right! I finally got around to messing with that plate on the side of the tranny, it was the problem.

there is no real adjustment however that I could see, only the fact that one of the two mounting holes for the plate is slightly eccentric, but did not give quite enough play to make a difference due to a mount locating pin that I contemplated breaking off.

so what I did was leave one of the bolts out, and then I had enough play to rotate it just enough so that reverse works at all times. not sure how it got out of range, maybe I was not delicate enough when moving the case around or cleaning.

oh well. thanks again for your spot-on diagnosis!