After ignoring this problem for some time, I opened it up again for a closer look, and determined that there is substantial play in the shifter 'Yoke Bushings' (#30 in the picture).
I ordered up the repair kit (#18), along with new linkage bushings (#282 some play observed), and I'll let everyone know how it goes.
"Everyone", meaning the 5 readers or so who have this transmission, of course!
Link to picture of shifter mechanism
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