89 5.0 AC help - O rings

I found my leak with the help of my HVAC buddy - the Oring connection near the firewall where dthe line connects. I picked up some No. 8 rings that look like the same size as the old ones (just a bit skinnier) but I cant seem to get get the line to reconnect. I am trying to avoid damage by not pushing too hard.
Does anyone know if that is the correct size? He told me that they may be the correct diameter, but the wrong ring material thickness.

Thanks for any help.
(I tried to search first)

Sounds like good advise on the tabs.
I am working out of town now, only have sat's to work on the car, will check that this weekend.
Keep the info comming please.
Thanks