GREAT NEWS - PROBLEM SOLVED!!

Well, wasn't too keen about diving into the old Baker-Hill 5000, but had some free time on my schedule so finally did so... Thanks to some great DIY guidance found on this forum and others, I was able to successfully just start tearing it apart "from the outside in" and pulled circlips and bearings and planetaries until I finally got into the guts of the transmission itself and FOUND the problem!

Although I'd initially suspected the shifting issue was caused by "worn nubs" on the shift fork, turns out they were in pretty good condition and still able to engage fully to move the shifter ring back and forth pretty easily. However, the shift arm itself was another story, as the little brass pin at the base of the shift arm which locks the shaft to the shift fork assy had partially sheared, which was preventing the shift fork itself to achieve full travel under load. Thus, when it "appeared" the shift lever was moving correctly when looking at the transmission externally, the sheared pin on the shaft was actually NOT making the shift fork inside move fully into the correct position - it was just slipping on the shaft enough to cause problems shifting and staying in gear.

After drilling out the remains of the brass pin, I replaced it with a stronger steel roll pin and the shifter is now functioning properly! And, after all these years of ownership, I was actually able to get a good look inside the transmission and confirm that all the other components are actually in very good shape! No major wear or corrosion or accumulations of crud inside, thank goodness! Just gave everything a good cleaning and flush, then topped off the gearbox with a heavier straight SAE 140 gear oil and we're now GOOD TO GO!

Thanks again to all who support and contribute to this forum and others, as I would NOT have had the courage (or knowledge) to attempt this repair without help. Happy trails to all!!