The clutch cover gasket is about $15 and the seal is about $12. I have not yet installed this seal in a KX500 yet. On my red bike it was very easy to do, once the clutch basket was out of the way. I was thinking it would be the same until I looked at the parts diagram. They show the seal on the inside of the case half. I will be watching this post closely to find out if it is replaceable without splitting the cases.
By the way, I had a red bike that ran real bad when the transmission was full,lots of spooge at the slilencer joint, after riding a half hour it ran great. When I got it home the transmission would be empty. Every time I filled the trans it would smoke and load up. It was sucking the trans oil through the seal. Simple fix and I thought I was a genius because I figured it out,after asking around I found out most two stroke guys already knew about this, and I wasnt so smart after all. John