Normally when one part in the head needs replacing there are others that are close to needing replacing. I would buy the standard Jabsco refit kit and replace all the parts that comes in the kit. It is very simple
I did this once. Sat on the dock with a toothbrush cleaning crusted salt and poop and the brush flicked stuff into my face.
yeah yeah, don't do that. duh.
Here's the thing though: the refit kit is like 60, and an entire pump is 99. (they used to be only $10 or so apart which made it a REALLY easy choice)
but even for $40, it's SOOOOOOO much better to just replace the whole thing
and yeah, after the second one died, I got a raritan