When I first drove this 1983 Porsche 911, I found the shifting to be difficult and it was grinding gears badly. My suggestion to the owner was to get in and replace the synchronizer bands before something breaks.
After taking it apart I couldn’t see much wrong and the synchros seemed used but not totally worn out. Like many other car manufacturers, the synchro for 2nd and 3rd gear is different than of the other gears and maybe someone put the incorrect part on the gears.
It wasn’t until re-assembly that I noticed that the dog teeth on first gear were chipped and remembered that the slider (operating sleeve, shift sleeve) for 1st gear has asymmetrical internal teeth to meet up with the corresponding dog teeth on 1st gear. The operating sleeve can be reversed so the side that should engage 1st gear is incorrectly jamming into 2nd which makes engaging into either of these gears while under motion nearly impossible.
Lucky for the owner, I located a shop who can replace just the dog teeth (engagement teeth) for short money without having to spend the $2000 that Porsche quoted to get the parts. We sent 2nd gear from a 901 transmission to the same guy for repair and cannot wait to see how they look and more importantly how they perform.

Transmission repair Porsche 911, 915, 901

901, 915, G60 transmission for Porsche repair