The discussion on oil bypass filters reminded me of an article in Car
and Driver last month. It was an interview with a oil chemist who was
discussing additives and corrosion in engines. When asked what he would
use for an infrequently driven vehicle (presumably like a lot of
Vanagons or Westfailias used only in summer months) he answered diesel
engine lubricant. These oils have much more anti corrosive additives and
detergent than gasoline oils so therefore protect better against
corrosion which he claimed was the problem. I checked around and their
are available 10-30 and 15-40 oils for diesel engines that are also
listed as suitable for gas engines. I'm trying it out now and will
report on any problems. The author mentioned that some engines seals may
leak with the diesel oils. The oils are more expensive marginally than
normal oil but less than 1/2 the cost of synthetics.