I could be wrong but from my own experience, the return hose from the head covers to the breather box were completely clogged with "oil mayo" last autumn and I burned oil. I could not blow through it with my mouth but when I put compressed air into it, the plug came out. Once they were cleaned, my oil consumption almost disappeared.
I would suggest you to remove the return hose from the heads and blow them clean with compressed air. At least it doesn't hurt.