After looking at your picture I would say wiredgorge is probally right in saying a compression check would give you enough info to see if that is your problem. Your pictures say you have a fair grasp on the technical end of things. But, if your ring seal is going and you have to get into it to fix it, it's not a bad idea to know where you stand on the topend seal. I personally don't use a compression test any more, guarantee it has the potential to fool a good mechanic if he doesn't pay attention to the tell tail signs. Many people already have a compression tester and it can be a good tool. Just don't assume that low compression numbers mean you have a bad ring seal.
Not trying to stir anything, promise you, but have had guys come to me with #'s saying this or that is my problem. A compression check is a VERY good way to determin overall condition of the engine, not the specifics. Compression ratio and camshaft profiles can play a big part in compression testing.
WOAH, just read my post, sorry, just came from the shop and my mind is going mach on engine works and theorys. Probally shoud delete it but someone may get some good use out of it. My wife wont, and she's the only other one in the room, for now.
Les Holt