On a 1986 mercruiser alpha one lower unit. Is there suppose to be a o-ring on the input shaft just below the threads? When putting my unit back together i installed the o-ring on the shaft then i installed the lower unit back onto the upper unit. I had to pull the lower unit off to double check something and the shaft no longer had the o-ring on. It was in the upper unit past the seal. Is that o-ring needed?
