The O-Ring At my Oil Filter Housing Keeps Leaking. I have replaced it twice now and have come to the conclusion that I’m not putting the o-rings on wrong and I have the right ones, lol. So I can’t figure out why they keep leaking. There must be too much pressure for some reason, 
. Attached are pictures I took from someone else’s post for reference of the area, and included is a diagram of the unit. #14 is my leak point.
You need to make sure the o-rings are Viton rubber and not Butyl Nitrile. Viton can hold up to the temperatures the oil reaches. The Nitrile ones will start to harden and get brittle. Good for about 6 months before they will start leaking. There is another o-ring not in the picture. It is between the upper and lower housing. In the picture you can see 4 bolts that hold the housings together. It is in between them.
Andrew - just a thought - have you check the alignment of the two parts to make sure there is no worn area making it out of round for an even fitting between the bore (female section) and the neck (male section) - also for any pitting on the surfaces of each part - as mentioned by Dick the Viton orings should seal better - Tex.
Is that O-ring 13?
Yes, #13. There is also one where the base piece bolts onto the secondary oil pan. Leave the 3 bolts somewhat loose when putting back together and tighten them last so the upper housing will be centered inside the lower housing. If not centered, it can leak as the #14 o-ring will be tight on one side and not the other.
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That’s the one I’m talking about, it’s o/ring number 14. The diagram doesn’t show the lower unit that it gets sandwiched between. I’m thinking that there might be too much pressure in the system, but theoretically the pressure relief valve should give before the o-ring does. I put the new one in and it was leaking 12 seconds later.
FWIW, these are the “O” rings I bought when I did the same job for the second time after using the “wrong” rings. No leaks since. (Yet!)
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Apart from Viton (FKM rubber) it’s wort checking the quality of the o-ri g itself. Any lips/irregular shapes means someone is selling you cheapest rubbish. How you’ve measured the size required?
If you buy from a reputable supplier, you should get good stuff. I got the measurements off of the original Jaguar o-rings out of a Genuine Jaguar gasket set. The ones shown above from the O-ring Store are correct and they have very good quality pieces.
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Should you measure the groove/lip itself and calculate it with oring calculator? Just to make sure that nothing went bad during… f.eg Jaguar’s weekend shift…
Google measuring o-rings if you like. The ones above in the picture are the correct size for the oil filter base.