05.5 950A w/ 18,000. I've been running into the same issue. I check my oil once every two weeks or so when commuting around town. Lately I find the oil level at 1/4 from max regardless if I have filled to 1/2 from max a few days before. Balance shaft seal? Front carb throat shows little to no residue. I do get a little smoke out of the exhaust at startup but it goes away after 10 seconds or so. Any thoughts?