1981 CSR1000 Stuck in 1st gear. Hopefully not Neutral Finder

Hey all, I know this question has been asked from about 10 different directions, but none of them seem to apply to my issue. My 81 CSR1000 (kz1000 with chrome spoke rims.) is stuck in 1st Gear. Clutch works fine as in it disengages when you pull the lever. Can ride fine in 1st, but the shift lever will not move. Clutch in, clutch out, rolling at 10-50 mph still shift lever will not move. Worked fine till yesterday, then stuck. Possibly stuck clutch plates ? I would think that the clutch wouldn't disengage then. Bike makes no unusual noise, just stays in 1st. Any suggestions besides splitting the cases and removing or cleaning those ball bearings? Maybe a lighter weight oil ? dude put 10w30 in it before I bought it.

Does it go into neutral? Put it on the high stand, 1st gear, clutch disengaged, running. The rear wheel may spin, but you should be able to hold it to a stop. If not, it's a clutch problem.

If good there, gotta pull the trans cover and inspect hardware. Next is dropping the pan to check that the the shift forks are free and undamaged. From there you can pull the forks, shafts, and shift drum.

Everything good at that point requires splitting the case to pull the main and counter shaft.. Can't even bench test shifting on these things because you need the trans at a decent speed to unseat the neutral finder balls before you can shift into second.

Could be as simple as a shift return spring. You'll have to remove the sprocket cover, sprocket and tranny cover to replace it.
Steve

It doesnt shift fo neutral, just 1st gear and no movement of the shift lever. Thank you for the info, I'll start tearing into it. I think the guy beat it a little bit so maybe a bent shift fork ? I'll take a look.

Tire doesn't even spin until I release the clutch probably because chain rusted to shit, Once I release the clutch spins after I pull the clutch back in, and I can stop it with my hand. Proves the clutch is working correct ? Time to take a look at the shift return spring it sounds like. I'm not Mr Super wrench, so I'm trying the easier possibilities first.

Thank you for your responses.

This might give you an idea how to go about it.
Steve