It's sounds like something is worn or bent but you won't hurt anything trying different types of trans oils.
Motorcycle transmissions can be fickle , so it might take trying a few until you find one that your bike really likes. Dexron ATF is an excellent starting point, given that automatic transmissions in cars share a lot of the same characteristics as the wet clutch transmissions we have in bikes. A high quality 10W40 automotive engine oil will also work well in a lot of cases. There are lots of great options. I've run Shell Rotella 10w30 in lots of transmissions over the years with great success.