1972 Chevy S-10 “Floating” manual gear shifter

I have a 1972 Chevy C-10 PU
(No C-10 on menu so I put this in under S-10)

350 CI, 4-Barrel Carb, 3 on the column manual transmission
No A-C, no power steering, no power brakes

Every once in a while when I am shifting gears, the shifting lever seems to land in "˜no man’s land.’ This first happened years ago and then did not recur for quite a while. I has now happened twice in the last week.

The first time I came to a stop light and shifted from 2nd into what I thought was neutral. While sitting stopped at a red light I heard a rattling sound that I could not readily place. The sound got progressively got louder (higher in pitch) and I think th eshifting lever started to vibrate. When I moved the shifting arm it seemed to be outside the normal "˜H’ pattern. By moving the arm around, I was able to get into 1st gear and move along without incident.

The second time I think I was trying to shifted out first into neutral after coming to a slow-speed stop. This time the gears for 1st remained engaged (which I was able to override by keeping the clutch engaged). I got off the road and was able to eventually get into neutral and return to the normal "˜H’ pattern.

I looked at the linkage coming from the shifting arm (in front of the firewall, inside the engine compartment) but did not see anything that looked particularly abnormal (no bent parts / no abnormal wear that I could see).

The rattling sound makes me think that the problem is associated with the transmission gears. I think it’s been 20 years or so since I have had the transmission worked on.

Any thoughts / suggestions as to diagnostic steps I may take. Are there adjustments that a mid-level gear head could attempt?