I purchased 2 fuel caps years ago to have if I needed them. They were the newer style that the back disc was threaded and had a nylon taper. I removed them from the box today to find the fuel lube that was applied during mfg was now a sticky mess and did not allow the cap to work properly.
My old caps that are currently in use needed a new shaft O ring. I have never had them apart and they were stuck. The old model used aluminum for the shaft and had reacted to the nut. I gave it a shot of Aero kroil and used a small impact to remove the nut. By holding the cap in my hand with the lever in the down position, I reduce the risk of breaking the pin.
The small O ring on the shaft is the one that will wear out. And it will allow water to enter the tank. It is also part of the reason the cap does not release when the tab is lifted. It also needs to be lubed with Krytox. EZ turn/fuel lube will gum it up and the cap will need to be pushed on to remove it from the tank. It can't be washed off, it needs to be removed by wiping it off with a rag and a lot of pressure.
Having dealt with both the old and new style, I will say, I like the old style better than the current style. The old style disc was not threaded and not tapered. It floated on the shaft and was held in place with the nut. It pushed the O ring against the taper of the cap and the O ring slid up the taper to expand. To adjust, all you need to do is tighten the nut with the lever closed and then try to press it into the tank with your thumbs only. If it won't pop in, loosen it up a bit. When it does go in, take a pen or something that will fit in the cap recess and try to rotate the cap. It should rotate just a little with a good effort.
The new style is the same except you adjust the threaded disc and when you are content with the fit, you bring the nut down to just touch the disc and keep it's position. The Nylock part of the nut is what keeps the nut on the shaft.
If you ever have to pry up hard to flip up the lever, it is time for cleaning and lube. If you ever need to press hard to latch cap, it's time for cleaning and lube. Under normal use, you should never break a pin. Doing so means something is not working properly.
I am not running auto fuel so the O rings were purchased at NAPA Auto parts
at a cost of .80 cents each for the small 727-2012. And $1.10 each for the big 727-2325 O rings.
The impact I used.... I don't' expect to need it next time. But if I do....
The lube highly recommended here on VAF...