Sea Foam is advertised as not hurting rubber, but there are a lot of plastic pieces in modern engines, and I would worry more about them than the rubber. Many of these plastics weren't even invented when Sea Foam was introduced in the 1940s.

A cheaper version, used many years ago, was to simply pour white gas/camping fuel into the engine, as it is a primary ingredient of Sea Foam.

I am not sure that we are seeing water come out of lubricating oil as with the jet fuel, I think the failure mode is that natural condensation in the engine crankcase (from repeated heating/cooling cycles) builds up and emulsifies with the oil if it isn't burnt off by getting the engine hot enough, for long enough, as it was designed to be operated. Short trips build up that condensate, which forms an emulsification with the oil, producing a cream-coloured paste with the consistency of Vaseline. If it is collecting under the filler cap, where it is visible, it is also collecting in the oil separator, where it isn't visible. If it gets cold enough, that emulsification/condensate freezes, as it has a lot of water in it. I don't think the water separates out, but rather it stays in suspension.

In my experience, if the condensate/paste is visible under the oil filler cap, you can clean it out with one or two hot oil changes in quick succession. The trouble is, if it stays there for any length of time, it has also collected in the separator and the only way to clean that out is to remove it.

I don't know whether Sea Foam or white gas would clean out the separator, but I tend to think it won't, as the separator only sees fumes from the crankcase, and not oil flow. I could be wrong on that, but I wouldn't trust an engine treatment to clean the separator the same as it cleans under the valve cover.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue