It's the vent that is troublesome to me. It is hard to tell where the seals are that might stop a build up of oil being exposed to the base of the piston. Perhaps, when it is operating, the crankcase is full of oil vapour which vents neatly at any angle and just settles when non-operating. Logically, as RCV does not warn against it, you should be able to mount it at any angle. And I am not suggesting you cannot. I would just like the comfort of hearing it from RCV as nowhere in their docs do they say you can even though nowhere in their docs do they say you can't. In an earlier message someone asked this question amongst others. The RCV answer covered everything except this specific question.

Just trying to be prudent here...