injector o rings

Hello everyone! 99 Grand Prix GT 130,000 miles. Just replaced the upper intake again(3rd time leaking coolant.) and this time I figured I should replace the o rings on the injectors. The Dorman plenum which it looks like they upgraded it since I last replaced it, came with the o rings for the injectors but 6 of them are thicker than the other 6. Which ones are the top and which ones are the bottom? I am guessing the thicker ones go on the top? Also I tried to get one of the old o rings off and the rim of the injector tip was brittle and broke off. I have read it is still ok to use since the o ring seals it anyway which is why I want to make sure I get the right thickness o ring on the correct side of the injector. Thanks!

I think you are right. The top of the injector is going to have high pressure and I would put the thicker one there. I would not worry about that little lip that broke off. When you put them in, coat the bottom o-rings with some motor oil. They will slide right in.

I ended up just putting the rail back in with the original o rings. I have had the rail out 3 other times and never replaced them but thought I should cause of the age but I guess the old saying is right "if it aint broke dont fix it" I have absolutely no leaks and wish I didnt try to pull the one o ring off which caused me to break off the tip. Thanks for the response!