this is what berkley says
Use 90 wt.gear oil check every 2 month or 100 hours of operation. To refill the bowl oil remove both of the 1/8" npt plugs on the bowl and using a squeeze bottle of oil force oil into one of the holes till it comes out the other, re-install both of the plugs. You may notice after a while that the bowl bearing area is full of water and not oil. This is a satisfactory condition, (it is best to keep full of oil) as water will leak past the seal, except that this water could cause structural damage to the bowl if permitted to freeze. For winterizing always re-fill with oil before lay-up of the boat. Both oil and or water will both lube and cool the tail shaft bushing at higher rpm levels. The bowl seal is more designed to keep the water out than the oil in as it is installed towards the pressure of the water. The seal will keep the oil or water mixture in the bowl area when the boat hauled out of the water as well.
