Q: My buddy has a Subaru Forester that I have replaced the fuel injector o-rings on 3 times now and it continues to blow the rings

My buddy replaced his head gasket, timing belt, radiator, plugs, and wires last weekend after it was all back together his injectors on the drivers side blew the o rings on the top of the injector he & his buddy who is a mechanic from out of town went to oreillys and bought felpro o rings said to be oem they put them on all injectors because he was worried that the other side would blow next about 2 days later they blew again so I replaced them for him this time because his buddy who is a mechanic went home out of town about a day after I replaced them the opposite side blew so I replaced those & those lasted a day now they have blown again I have checked each time I had done them that they are seating correctly in the fuelrail and are even I tighten them down a little bit on each side so that the pressure is evenly distributed as intighten then to insure they correctly seat I have noticed though that the felpro orings I have bought that say they are "oem"are tad thicker then the stock
My car has a manual transmission.