It may or may not be that seal. There are a few other common spots for leaks like the gasket under the front plate. First thing is to verify where you see leaking oil; In front at the base of the bezel, in back under the helm or around the shaft seal itself. Leaks from fittings can occur but would be 'visible' on the back side. To see if the shaft seal is leaking you have to usually pull the wheel. Note that if you over fill the unit, an easy thing to do, it may leak when operated or when it gets warm outside. In that case, it will seep from the filler/vent cap. if that happens, oil leaks but the operation of the steering is not affected.
If you don't see oil anywhere up front, check the steering cylinder piston seals and aft fittings (including bleeders)