Disclaimer: I only converted my Raidons to oil as an experiment, because otherwise I was going to give up on them. Definite improvement, and 6 months on they are still going well and no noticeable leaks. OK, with that in mind:-
I didn’t add any foam rings or anything, just dismantled, cleaned out the lowers and cleaned up the stanchions, reassembled and then squirted about 20ml of car oil (5w30 semi-synthetic I think?) in through the holes at the bottom of the lowers (while the bike was upside-down obviously), using a (clean) syringe from a brake bleed kit.
Obviously I wouldn’t advise this unprofessional approach on an expensive fork….