I've had a stash of Coleman stove fuel since before Y2K and decided to test some of to see if it would still burn properly.

I have two Coleman Peak 1 single burner stoves so out on the back porch I put a few ounces of fuel in each (they'd been burned down to empty for storage in the past) and pumped.

The oldest one pumped up, started and ran fine.

The next one wouldn't pump up. Couldn't get the pump to 'catch' at all even with oiling.

So off to REI for a pump repair kit.
The blister pack kit was ready to go for the long-shaft pump with plastic collar. It had other parts for other stoves but disassembly and reassembly was required.

All I needed was the rubber cup and retaining washer.

The rubber cup on my stove pump had worn down to the point it wouldn't work. That stove did the workhorse job in many backpacking trips so saw a lot of use.

Learned- (1) replacing pump cup and washer required needle-nose pliers. My normal backpacking kit would not have had the tools to use these parts even if I'd carried them.
(2) blister packed kit pump shaft is too long for the single-burner stoves.
(3) Just because the pump was working when the stove was put away, you can't be sure it will run next time if there have been many strokes applied to it.
(4) I didn't pay much attention to oiling the pump that failed and it had had gas wash it out one time so lack of lube probably contributed to the failure
(5) Coleman sells cups and washers on their website for less than the kit at REI. The REI kit has many unneeded parts.
(6) the old gas seems to be ok, at least for burning 20 minutes' worth.
(7) The Coleman website shows 4 or 5 models of single-burner stoves and calls them out by Coleman part numbers. But those numbers aren't on the stoves themselves so you have to make the best guess you can. I found that several stoves had the same part number for pump cup so little risk to using that number.

Simple summary- test your stuff periodically, have spares, learn what it takes to install the spares.