o-ring

Does any one have a good recommendation for fuel injector o-rings for our are cars? or will any brand basically do the job? I have a pretty big gas leak to the point where all i smell is gas while driving. i know i also have an exhaust leak and the excess gas (if i'm running rich) could smell...

Trying to replace the o-rings. The unit sits on a pedestal that is attached to the block. there are 2(two) 10 mm nuts underneath. Not easy to get to but I was able to get them loose. Then at the back, in very close proximaty to the firewall there is an oil line. I can not get this loose...