Tearing down the motor I found #3 intake lifter is extremly difficult to get out, all others came out like butter.

Story behind these lifters....
I bought a set of "new" Comp 850-16 lifters off ebay for a good deal (this was a store that sold multiple sets). They supposedly came straight from Comp. I got them and they looked used (oil stains and possible marks on the rollers) so I got in contact with the seller and they got Comp to send me a call tag where I sent mine back and got another set, I sent these to Comps address on Democrat Drive. The second set wasn't much better looking but I had a call tag from Comp so I figured it was legit. Now I have a cracked lifter and the motor was running like crap.
The lifter is cracked down by the roller.

Would a cracked lifter cause low oil pressure?

Are Comps lifters marked anywhere to distinguish them as Comp pieces?

1. Only if it was carcked through to the oil chamber or the oil passage, and the crack could bleed off more oil than a main bearing or the like. In other words, probably not.
2. Some of their lifters are laser-etched with the part # in the oil band around them. Don't know for sure about the 850. I don't have a set of those on hand to look at. I have some other part #s of theirs laying around though, I'll look when I get home. You could call them and ask.

As far as the replacement lifters being "legit", that's REALLY hard to guess at. Anybody can ship anything to anybody else, so just the act of shipping the first set to Comp isn't a guarantee of anything; unless the eBay store was somebody that has a legal connection to Comp (which I believe there is such a store on eBay, though I'm not positive of that). But, if the store is NOT legit, and they're picking up used factory lifters from somewhere and passing them off as new, then to keep from getting negative feedback or other problems, it might be cheapest for them to basically eat a set of them by having you ship them to Comp (basically, launch them into a black hole, as far as they're concerned) and at least put on a show that way. Frankly though, I can't imagine even a legitimate eBay store having Comp handle warranty claims DIRECTLY; that's not the way things are usually done, on eBay or anywhere else. Doesn't sound right to me.

my comp lifters had no stamping to prove it was theres. mine were new, and looked new, nothing you speak of. I purchased the magnum lifters for the ls1. they work fine in our cars.

I didn't think all lifters were stamped Comp but who knows. I don't know if I should just replace the one or all of them. $300 is quite a lot.