(and why would the rings in one cylinder wear dramatically more quickly than those in the other?). Obviously, as I tear into it, I'll closely inspect the head, head gasket, and the top surface of the block.
All of that, of course, unless one or more of you can give me a better approach.
Valves not seating. Excess fuel comes to mind also. I think having the pump and the injectors checked would be a good idea if you have a pump shop handy.