I'm not going to go into the pro,s and con,s of WD-40. But I will address the subject of lubricants drying out,turning to varnish and gumming up mechanisms. This happens to all petroleum products, even fuels. But for this gumming up to happen, on its own takes a fair amount of time. Add dust and dirt, foreign material, and powder residue it speeds up the process but it will still be well over a year or two.
I then ask the question as to "'how often do you clean your guns? Not just the barrel or a wipe down. How often do you strip the gun down and really clean it?
Its a pro-active preventive maintenance schedule, instead of a re-active maintenance necessity because its gummed up. If you feel that your life depends on the reliable functioning of this gun, then you would be wise to set up a periodic maintenance schedule on it before it has time to gum up.
You change oil on your cars for the same reasons, only difference is the car has a drain plug, although sounds like a couple guns probably need one. I've never seen a gun with so much oil that the cartridges were ruined. " there"s your sign", not enough attention given to the gun.
If you have time to do it twice, then you have time to do it once right and put your name on it