When I replaced the seacocks on the toilet inlet and outlet on my B34 last year, I considered what to do about the engine raw water inlet. Firstly it has always remained smooth to operate since we bought the boat in 2001. Secondly there is unlikely to be a problem with this fitting as it is connected to the saildrive which has its own sacrificial anode and is in electrical isolation from the rest of the boat.
Having had this thought process I feel confident not to change this seacock, but I will inspect the hosetail above the seacock each year as part of my service schedule as the hosetails on the toilet seacocks were only brass and had deteriorated.