i can guess you are right when you talk about the seals being scuppered, if you replace the rubber parts (which by now have probably degraded one hell of a lot, what with what seems like both continuous use and lack of a bit of TLC ) then that will solve the lack of power problem, possibly even some other problems as well as it may slow down the cycle better and stop any kind of violent cycling and double feeding or jamming if the o-rings are tighter.seems gas it going everywhere
with a bit of help you may be able to make these parts though instead of trying to import them, Now all we need is a person who has experience with machining rubber parts to see this thread and post..... fingers crossed....