I have had one the old yellow back pack from WCW for years and they are badly put together. I have rebuilt my one and it been a dream still working after 7 years. I have redone all the wiring, replaced the pump and fitted a larger 12-hour battery and it`s never been better.
Sounds more like triggers broom
I used to have one of those too
About 3 years ago I replaced it with one from Gardiners ( with the stupid blue handled lid that I modified by adding a better handle )
the pump would make an awful high pitched screeching noise when used on lowest setting when you stopped flow between windows - there was an adjustment screw for pressure switch - that worked for a while and then speed settings stopped working - now only works full speed but pump doesn't always sound right, think it maybe on the way out hence my post .
I'd sooner buy a new one before its needed than have the thing go completely on me.
I could do what you have done but for £100 I can't be bothered. If I can get 3 years from a backpack I'm happy.