So I went and checked out a 1983 XL600 this weekend. I was able to get a few rides in. I didn't hear any knocks or ticks from the engine. There is a little more than 15,000 miles on it. The shifting was smooth and I didn't feel any difficulties in changing gears. The only problem I noticed was a small oil leak. The location of the leak had me wondering. The guy selling the bike says it's from the frame and not the engine (head etc). I saw that the oil leak was around the top of the engine by the spark plug. So my question to you guys, is it common to have the frame (I'm guessing he meant the hose coming from the frame) leak oil? If so, how expensive of a fix is it generally? Thanks.