The issue with them is that they are just not quite thick enough to get your interference fit of the mag into the breech (you would actually want 5mmx2mm x something like 1.8mm instead of the available 1.5mm). So I used a small dab of a thick adhesive (I used E6000, but any of the 'Shoe Goo' types would work) to hold it in place and lift it just a bit. Works just like the OEM one now, and I never have to worry about another one falling out. Plus I got a whole bag of them now, so I can quickly and easily replace any which get torn up, etc. (but none of them have yet).
You look up all the orings needed for you wildcat plus other pcp's you already have and order everything online. It will cost you about 40 or less and you could rebuild all your pcp's 5 timed