I had one like that. I think I used a wooden dowel and hammer on that little tab on the underside of the endcap. Just enough to move it so I could get a flat screwdriver blade in the gap, top and bottom, to wiggle it off.Once you get it off, use some sandpaper to slightly reduce the diameter so it slides on and off easier. Easy sanding, it's aluminum.
...I first tried a new lead one but could not get it to hold air overnight.
LOL.... I don't have the energy to pump one 10 times... no danger in that happening.
Welp, guess it's time to get some liquid wrench. Can't get this thing to budge for the life of me.
... The heavy, close fitting long lever was the key to breaking it loose for me. I first stuck a screwdriver through there but it did not have enough leverage to break it loose.