Erratic Oil Loss

This is the strangest thing I've come across yet. I have a new-to-me 82 1100I. I check the oil every tank of gas. Most of the time the oil is spot on, no loss. But twice now I've lost an entire quart of oil during the tank.

I cannot correlate this loss to anything specific in my driving. The first time it had happened was after 700 miles of commuting, I checked the oil, it was fine. I took at 100 mile country drive. Before I turned it toward home (the engine was cold!) I checked the oil and holy smokes, I'm a quart low. Must've been something strange in the 100 mile run. Extended run at highway speeds, right?

Well, wrong. It didn't use any oil on the return trip. Even though it was the same distance and same type of ride. Perplexed, I vowed to keep a close eye on the oil level.

I did another 650 mile drive, and drove another 200 miles of commuting traffic, and didn't lose any oil. I checked it after every tank.

Then, this last tank, all commuting traffic, I lost a quart.

What gives?

I should mention that the head covers do leak a small amount of oil. I plan to replace the head cover gaskets. The previous owner must've bought them fancy new chrome head covers and put them in place with old gaskets. The only evidence I ever see of this leak (unless I lie on the ground under my bike and look up) is a little quarter sized spot of oil on my left boot from tucking it under the head cover while shifting. I know this obvious leak seems like a likely culprit for my oil loss, but it doesn't quite add up. I see the spot of oil on my boot yet I consistently have good oil level for tank after tank. Then, all at once, in one tank, I lose a quart. If it were a consistent loss rate it'd make more sense to me.