Although head maintenance is low on everyone’s fun task list, working on functioning head that has been flushed clean (flush with lots of clean water, soak in vinegar for 15 minutes, and then flush that through with more water) head is much more pleasant than working on a broken, clogged head.
Joker Valve. If you have a Jabsco Manual or Groco Manual head, install a Raritan joker valve. It is dimensionally interchangeable and long term PS testing has confirmed that they last about twice as long. The price is a bit more, but the total cost is less and the improved operation and reduced labor is a blessing. The joker valve should be installed with the lips vertical; placed horizontal, they droop under gravity and fail prematurely.
Lubrication. Follow the manufacture instructions, giving the pump a good slathering of synthetic grease every season (every other season, if use is light). Break the cooking oil lube habit; it’s bad for the holding tank and marginal for the pump.
Replace vs. Repair. Jabsco sells a rebuild kit, but at 70 percent of the Amazon price of a new pump, its a poor investment. The new pump will last much longer and is much easier to install than the kit. Raritan heads are easier to rebuild, and the results more durable.
Preventive maintenance is the key. Motivating yourself to actually do it is the challenge.