Not a lot of maintenance required. I get them, test them, change all the reasonable orings and they are usually good for a few years.I say this as I am in the middle of changing out some leaking O-rings…if you have the time to keep all of them up to snuff, well more power to you.
Other than the Invader, I broke it a couple years ago and it has only ever worked as a bolt action since.
Gotta get the Hartley and Falcon out. The British lovelies need to be fondled and fired.