The back side of the thrust bearing will be polished from the clutch fork pushing the crank forward every time you shift. That's normal, as long as the end play isn't excessive. If it's got .010" or less end play, no problem, and I've seen engines with a lot more.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!