“I have an HP 4000 purchased in 1999.”
My experience with hp isn’t quite so good, but it is probably because 1995-2002 I lived at the beach and the way every OTHER piece of metal corroded, I suspect this wasn’t optimum for the insides of what I *think* was an hp 2c or 2p. It started out pretty well but the every-four-month $160 repair routine got old quickly.
I agree that off-brand refills, for many years, just sucked. Recently I have had better luck with refills from Cartridge World. OTOH, if you are getting that many thousand pages from a genuine cart, it seems like false economy to try to save a few bucks. I’m not exactly head over heels with the idea of refilling them myself. It’s one of those life-jobs I’d prefer to delegate!
I have an HP 2p in the basement. Great little printer and got a lot of use out of it but it now prints solid black on every page.
The 4000 is an office, not residential, machine and I think HP built them with higher quality.
And, as you say, salt water atmosphere and high humidity is not great for printer life.
Jack