You could try a compression/leak down test. This should tell you if it is rings or guides. While I had the heads off I would throw a new set of rings in it anyway. If it has lots of miles on it, it probably wouldn't hurt. Rings and a hone job if you can do it yourself is very cheap. If you do a valve job make sure that they put in new valves they are also cheap to buy. I do a lot of work on my own bike too. I hate to have double work. I just want to ride the dam thing, not wrench on it.
Good luck and ride safe!
Hope this helps.
Lenny