Look closely at the dogs on the sides of the gears, the lugs that engage and hold it to the gear next to it. If they are worn at all that will give you trouble. Rinse some acetone or brake cleaner over the top of everything so it's real clean and easy to inspect. Also check the fluid for big chunks or slivers.
By chance, would you happen to have a picture of what the "dogs" look like? I looked down into the gears last night after removing the shift forks and didn't see any visible wear, but I have not drained the fluid as of yet. What the fluid is covering (bottom half of gears) isn't something I would really see anyway even if it was drained. I'll drain the fluid tonight and inspect for the chunks/slivers.
No picture, but when the forks slide the gears over, the gears have lugs on the sides that engage the gear next to it. If you slide the gears around they are very obvious. Drain the fluid for sure, how else can you see into the bottom?
I assume that when say Pawl,you are talking about the shifter drum??
there is a spring loaded detent that keeps it in position
maybe, just maybe the spring is broken, allowing the drum to rotate without using the shifter pawl