HI scrit. Just regular old 80-90w lower unit oil is fine. They sell it at wal mart and a lot of auto parts stores too. Yo;ll probably need to get one of these little pumps too. They should sell them right next to the oil. However, I did just come across this article that sounds interesting, considering a lot of vintage motors have leaky lower units, even after a reseal job. I haven't tried it personally, but it is intriguing.