eb,
It sure does sound like a guide or stem seal issue, but I wonder if the PCV valve could be involved somehow. Has it been replaced lately?
Rings usually don't exhibit smoke sporadically, but if one is sticking, it's possible. We always pinned the problem on the guides if the engine would lay down a smoke screen after running down a hill under compression, then hitting the throttle. Will your rig do this.
I don't know how bad the engine was pumping or leaking oil, but if the muffler was inundated, it can take longer than one would expect to cook it clean. Keep us posted.
Stuart
