One other thing that I'd consider common with age when the primer never becomes firm with pumping is that the fuel pump diaphragm tears and no longer pumps. When this happens, fuel goes right through the diaphragm and into the crank case through the impulse hose (the small fuel line hose that supplies in/out crankcase pressure that works the fuel pump's diaphragm to pump).
Don't know if yours is bad (yet), but if you run into issues getting primed, this can happen. Age and gas and rubber don't get along well. I don't know how long these last, but diaphragms are definitely not 30 year items. At least none I've seen. I consider it near the top of the list of things to change on a new old Force.
