[FRED/LI]

I'd hate to lose that beer, but you may be able to check the spark plugs to potentially isolate a particular cylinder or determine if it's all six. in that case, I'd lean towards the induction system if all are showing some discoloration. Worst case, rings are worn and letting oil by.
My SC from years past was torn down not too long after I sold it and the piston rings were too weak to even spring out when the sleeve was removed. It too, exhibited the same symptoms you describe.
I'd still bet that it's in the induction or venting...at least I'd hope to find something there.