Motorcycle Repair: losing oil, combustion chamber, leak oil

Question
My bike is a 1970 Electra Glide, FLH.  I go through a lot of oil and would like to understand why.

I have a small crack in the inner primary housing that leaks a little oil when I park the bike, so I always check the oil level before riding and I keep a quart in my saddlebag, just in case.  
Recently I went for a group ride and was told I was burning oil.  After about 100 miles the level was so low that it didn't even read on the dipstick.  This seems like too much loss for it to be just the inner primary.

So, what do I need to have a mechanic look at/ look for?

Thank you in advance for your advise.

Answer
If you are burning oil then you probably need the top end done. You can lose oil through the valve guides and the piston rings. Both will leak oil into the combustion chamber and burn with the gas. You need to pull the heads and cylinders and do a  inspection.
Good luck and happy riding