The seacock has an elbow
. I took pictures of all the seacocks and parts
when I disassembled them, cleaned, then reassembled. My pictures of that plug show no obvious pitting. To be fair, by "service" it means I disassembled, cleaned (case, inside, plug) lubed and reassembled.
Re: possible draining back from engine
. I think this is not indicated given I can increase or decrease the flow by moving the handle on the seacock. If the valve closed fully the water draining back from the engine should not be affected, and certainly not keep on running for 15-20 mins.