81 KZ305 using alot of oil

It uses a quart every 250 miles. Does not smoke at idle. Don't see smoke in mirrors when riding. Doesn't leak.
Before I take the top end apart, is there something besides valves/seals and pistons/rings that would cause oil consumption?

It can burn oil without generating a lot of visible smoke, especially while you're riding. How do the plugs look?

Given the age of the bike, my first inclination is the valve guide seals have failed. The rings are less likely to be an issue unless there are a lot of miles on the bike.


 

The bike had 6,000 miles on it when I got it 2 years ago. It now has 8,000. It has used oil at this rate since I owned it. The plug electroids and insulator are tan. The metal base is black.
Can the valve seals be replaced without femoving the head?

They cannot, but the 305 engine is very easy to take apart and reassemble.

Leaking from somewhere you can't see?

Not motorcycle, but I was chasing a oil leak on my 86' Monte Carlo SS with stock 305. For the life of me, I couldn't find the oil leak but I knew it was leaking as it does not burn the oil (checked both the exhaust and plug). No oil trace on the ground. Found the cause was oil leaking from back of the intake manifold and oil was dripping on the hot exhaust. I smelled the burnt oil but I always thought it was from car next to me as when I parked my car, I couldn't smell it.

Just my experience.

Run straight 50 weight in it!
Or,
Motor Honey!
STP!
Bardahl
Saw Dust! 
Lucas!