Generation III Internal Engine - oil pickup tube o ring question

I have a 2000 camaro ss that I'm putting a cam and timing chain on. I went to replace the o ring. The one that came off is grey in color and sort of flat on the inside and outside, compared to the new o rings which are completely round. I do have new o rings that came with my timing gasket kit, but they are red, black and green. None of them are the exact same size as the grey one that came off. I have read that my engine (2000 ls1) should of had a blue o ring and that they may be replaced with the thicker red o ring. But with mine having had the grey o ring, I'm not sure which one to put on. Just try the red one and see how the resistance is or??
Thanks for any help.

The one I removed was greyish, as well. Could have been blue when it was new...I don't know. Also, your old one might have been flattened somewhat.
When I ordered a new Melling oil pump, it came with a green & a black o-ring. I was instructed to use the green one for a LS1.
The green one is thicker than a blue one, which came with another (blue o-ring) oil pump I already had.
So, I wasn't sure either.
The green will fit, although it will be a bit tighter.

the really fat thick one is for the truck pick up tube's. the thinner of the two o rings is for the F-body, Corvette pick up tubes. this will answer your question:
http://ls1tech.com/forums/generation-iii-internal-engine/1473076-oil-pump-o-ring.html

Alright so I guess I will try the green one first and if I have to use too much force to put it on I will try the black one.
Thanks guys!

Hey guys, just wanted to add...after examining the instruction sheet for a new Melling pump, the sheet shows two diagrams, but doesn't specify truck or passenger car LS1.
The instructions show two diagrams...one of them looks like the LS1 pickup tube (with the 'lip' on it). To this one, it says to use the green o-ring.
The other diagram has a pickup tube that I don't recognize. To this one, they use the black ring.

http://ls1tech.com/forums/conversions-hybrids/1401786-help-low-oil-pressure-new-swap-2.html

Post #35 has pics of both the truck pickup tube and the car pickup tube with and without the O-rings.

I don't know why melling even puts those instruction in the box, i found them to be very confusing.

why buy anything other than GM gaskets?

12557752 is blue, GM sells em 5 to a bag

this is for the C5 p/u tube

people often fck up the Oring, loosen x4 OP bolts to block.........then tighten p/u tube....tighten OP

Orings are like ladies, they are not fun when your trying to get things together dry