O-ring rebuild kit - Steyr LP-10/LP10e/EVO.
LP10 Manual part # 7    - body to bolt seal - 3 ea
LP10 Manual part # 29.9 - cylinder to inlet seal - 3 ea
These two parts will receive by far the most wear and tear during normal use of your gun. Every time you remove/replace the cylinder part #29.9 will be strained, and EVERY SINGLE SHOT you take will put compression and sliding friction on part #7. Multiply that by five to ten thousand shots (with a couple hundred air changes along the way) and these two seals will be the first ones you notice starting to fail.

LP10 Manual part # 71   - bolt to barrel seal - 3 ea
This one is the most likely to be overlooked, because it's hiding in a place you might never see, but every time you force the bolt closed for a live fire shot this part will be placed in compression. Because it doesn't see the sliding friction of the other o-rings you might not notice the same level of deterioration, but over time as the material hardens it will lose it's ability to expand back to it's spec dimension. As this happens it will lose its ability to form a proper seal, so I recommend that this o-ring be replaced at the same time as #s 7 and 29.9.

LP10 Manual part # 13   - regulator to body seal - NOT NORMALLY INCLUDED, REQUEST IT IF REQUIRED.
I've seen this included in some "full rebuild" kits, but the only time you might need this is when you need to pop the regulator body off to access the valve/spring assembly. Normally that type of work is best left to the techs at Pilkington or Steyr, so you shouldn't need this o-ring from me. If you really want one let me know and I can throw one in your order for you, but because this one is a static seal that doesn't see any of the wear and tear of the others, I'd advise leaving it alone.

Installation:
Using a dental scraper makes removing your old o-rings a breeze. Installing #s 7 and 71 is pretty straight forward, just press them in and go. Part #29.9 takes a bit of force to get back on but once you get the technique down it's easy enough.
https://www.amazon.com/gp/product/B07SLZ2RQL
https://www.youtube.com/watch?v=gUl4fPRtnic

Proper storage between sessions:
It's recommended that you not store the gun with the bolt fully closed, as this will force the o-rings into compression and in the long term will lead to a loss in performance much sooner than you would normally expect.

To grease or not to grease:
From my experience in other industries I'm a big fan of the use of grease on o-rings, especially in cases where the o-ring will see a lot of sliding friction (like say, part #7), so whenever I install a new o-ring I give it a quick rub down with a small amount of grease. In addition to helping with longevity the o-ring will also have a tendency to absorb some of the grease and expand a bit as a result, helping with sealing. From there, periodic reapplication of grease can help sealing and lifespan. These guns run just fine with completely dry o-rings, but a little lube never hurt anyone! Something like a Dow (Molykote) 33 or 55 would work great.
https://www.amazon.com/Corning-Molykote-Medium-Grease-Lubricant/dp/B008ZG8V2U
https://www.amazon.com/Dow-Corning-Molykote-55-Grease/dp/B00B2OHYMU

"The one on my gun is green, but yours is black, what's up with that?"
I don't know! They're the same dimensions as the factory ones with a similar (if not identical) durometer, so they do exactly the same job just with a different look to them. If it makes you feel any better I've been using them in my personal LP10 and have made it through thousands of shots (and counting) without failure.