o-ring durometer / quality questions

So, I'm the new "techboy" for my student paintball group, and we have roughly 16-20 tippmann 98's that we use as rentals..

Therefore I need to get me some orings for the tippmann 98.. And after checking out the prices on OEM orings (those you get from tippmann themselves) I almost had a heartattack! I can get several hundreds of orings for the price of 1 or 2 of those kits..

I just need help to figure out what durometer and quality the different o-rings are.. How do I do that?

I have a few of those kits already, so sizes is no problem, that I can measure.

btw, I'm ordering from mcmaster.com so there is my reference

.ebo

Most paintball orings average in the 70-80 durometer range.

The Buna-N or nitrile (black rubber) orings are softer. They seal better over imperfections than does the urethane or harder (higher durometer) orings. But the black orings tend to be less forgiving. Meaning that they freeze when you unscrew your bottle of CO2 and then will never seal properly again.
The white urethane orings or clear urethane tend to last longer and are generally easier to maintain.
Urethane for the bottle, Buna-N for everything else...in a tippmann...that is a generalization but it usually holds true.

The bottom right one is the one that goes around the drive spring behind the rear bolt.

ok so ive got a pro/carbine that i took apart to clean and lube but when i took the reducer fitting off for the valve the o-ring shredded(that really small one)...so can i just put an o-ring from a normal kit in there or do i have to buy a special tippmann o-ring thanks guys