Re: checking level of lower unit oil
Welcome to iboats!
Both screws in the lower unit (top=Vent, bottom=Drain) need washers or rubber O-rings. Some lowers use washers, some use O-rings. If the screw has threads that go all the way to the screw head, you'll use washers. If the screw shank has an unthreaded area just below the head, you'll use O-rings.
If that top screw did not have a washer, it's best to drain the lower unit (remove both Vent and Drain screws) and replace the lube. Inspect used lube for water intrusion. Water in the lower unit lube will look like a whipped milk shake if the motor was recently run.
To refill, lube is squeezed or pumped into lower unit until it appears at the top Vent opening. Replace the top screw first. This creates a vacuum that holds the lube in the lower unit until the bottom screw is replaced.
Using a small pump (approx cost 10.00) is the easiest way to replace the lube.
Replace the seals with every lube change. Leaking seals is the main reason for water intrusion into the lower unit.
