My 1985 18' Advantage ski boat has the 3.8 litre V-6 with the OMC I/O. The outdrive unit has lower, intermediate and upper gearcases. It calls for OMC Hi-Vis gearcase lube. I'd like to replace the oil with something over the counter and not specialty marine oil that costs so much more. Can I use regular 75-90w gear oil? Any recommendations?