407079 replacement for the large #12 is not the right size.
this is not saying that you cannot get it to seal, but if you tried to wrap it with teflon tape it might seal too if you try hard enough
this part number is not correct, it is .008 in cross section larger and would not seal on my car.
the parts I listed are the correct parts, identical in diameter and cross section.
Interesting. I looked back and saw your post noting you had trouble. So since you noted this as a standard #12 O-ring, I went back and cross referenced the napa part for a standard #12 o-ring (AC Delco 15-3615) which is a different napa part # - TEM 407012. I didn't originally source it as a standard #12 because Lotus doesn't denote it that way in the service manual, instead by id and od with no cross section, so I found an exact match for the id/od stated in the manual but could definitely have had an incorrect cross section. Though I didn't have any trouble with sealing on my last endeavor with those but could have just been lucky on that.
If it is indeed a standard #12 then 407012 is actually the correct part number. So I'm on my way back to Napa, thanks for that info, it's all making sense now.
Now that I realize they are all standard sizes I cross referenced the others - 407006 is in fact the correct part # for a standard #6 o-ring. And 407008 is the correct part # for a standard #8. So those should be good.
I did not replace anything that required a #10, so I don't have a part # for that. Maybe that came from another post.
But if you look at the pattern to the standard part numbers for Napa O-rings 407-xxx , I'd put money the #10 o-ring is part # 407010. Its too bad the guys behind the counter don't know these things.
Thanks again for the info.