On a mono-valve (no seperate passenger and drivers side control) system like yours, it really sounds alot like the push button panel is going bad. The solder joints start to fail and cause intermittent problems like this. A bad vacuum element complaint is usually about one outlet not working at all.
You could try to save money and get a reman push button panel. I am unaware how much new ones are going for now, but a new one would be less of a "?" as far as the durability of the unit. Typically MB won't offer a particular item as a reman unit if rebuild isn't very feasable or the durability of a reman is questionable. I have replaced several push button panel in the shop that had "remanned by:" stickers on them, of course I have replaced many more original units, but the point is I don't believe the reman units were nearly as old as the original units I have replaced. It's a gamble is the long and short of it, but if it is junk immediately I am sure it is guaranteed at least for a while. The MB part I believe is guaranteed for 1 year/unlimited mileage.
The oil burning problem I really doubt is the head gasket. Usually the first sign of a blown head gasket is either external oil leakage or the introduction of oil into the coolant, so be alert for these developments. Could be the oil you're using. Do you see any signs of blueish exhaust smoke? At this mileage, valve stem seals are a distinct possibility. Usually when this is happening, you have cold start problems, what is usually described as a "false start". It seems like it started, but you stop cranking and it stalls right away, then starts OK on the second attempt. Pulling the spark plugs usually shows not an oily deposit, just kind of a normal-looking deposit, but rather heavy-kind of a grayish or yellowish looking deposit. If you think you are leaking the oil out, then check the front cylinder head cover "lip" seal, you will see oil on the right side of the engine, starting at the front between the head and block.