Some advice and some questions
Compact marine toilets--Jabsco, W-C Headmate, Groco HC HE HF) have an average lifespan of 10 years or less...so if the toilet is original on a 23 yr old boat, it's way past time to replace it....not just the pump, but the whole toilet...and now would be the ideal time to upgrade it to a PH II or PHC. I'm not surprised that it's loose and sucking air...'cuz the inside of the pump cylinder has become so worn, scratched and scored it can no longer pump efficiently...and because the cylinder is so worn, new seals, o-rings etc won't help.
You say you have a smelly head, but you don't make it clear whether it's just the toilet that stinks or the whole boat, or specific areas in and out of the toilet...So how 'bout a bit more detail?
You asked if changing the hose will help...if they're original, I wouldn't even bother to test 'em for odor permeation...'cuz 20+ year old hoses have got to be so hard, dry and brittle by now that they're a disaster waiting to happen. However, if they're relatively new, test 'em for odor permeation...which may not be necessary if the lockers they run through stink.
Do you have odor in the area where the tank is? if so, is your tank plastic, aluminum or a bladder?
Is there a macerator or manual pump to dump the tank installed? It could be one of your culprits. (You can't legally use it in the Bay, so whether it's a problem or not, it should be removed.)
Depending on your answers, your best course may be a complete new system--toilet, hoses and tank.
And btw, there have been several "head" threads lately...apparently you're not reading the right forum. The HeadMistress forum is specifically about heads and odor.
