My '72 seems to have lost power over the last few months. Today I noticed moisture being vented out the top of the valve cover. Other symtoms include backfiring through both carbs upon acceleration, though the engine seems to idle fine. I've checked the dipstick after the car has been run for foaming, and find none. I'm baffled and am wondering if a compression test on each cylinder will verify a blown head gasket. Any thoughts?