Don't know if this is relevant, but I've got a 20 year-old "Powermaster" 66

, which tends to sit neglected in a cupboard for years at a time - only being brought out when needed, to "take out" the occasional mouse that gets in the house or loft & refuses to be "trapped". Use it because on low power, it doesn't make a mess (or holes in the woodwork). Any road up - after sitting for so long between uses, the seal in the pump tube dries out/hardens. As a result, the lever goes all floppy (Oo-er). After putting a few drops of silicone oil in the tube and a minute's flailing of the lever, it starts to build up pressure. If I then put about 6/7 pumps in it, then secure the lever with a strap, on the last stroke at about 45 degees, so that it's straining against the pressure - I find that after being left a few hours, it's as good as new. Until the next time.
P