I use Marvels Mystery Oil extensivley offshore and would recomend it to any one, its great on freeing mechanical devices such as air starters, froze up motors and what not.
I've had two 318's that sat for 15+ years, one of which was stuck like a rock, poured a little Marvel down the spark plug holes, let it sit a few days. Both broke free, got both running great and drove one of the two 40,000 miles without a problem. Great stuff!