White rubber ring kit. There is no official ring list, this is what was in my machine.

A few notes about this kit as there are a few user-made kits on this site. I originally chose this version as I appreciated the user's time to create a schematic. However, after following his guidance and purchasing these sizes/quantities, I received a kit that will now require a second order to correct some mistakes.
1) It mentions to buy 11 of the 5/16". However in his picture, look at the only 'B' designation on the LHS of the playfield, at the left side of the Extra Ball lane. There's clearly a 5/16" rubber also on the other side of the opening to the Extra Ball saucer. If you try to use item G above it and pull it over its intended post and wrap it around this end post (where I believe another 5/16" belongs), you risk the metal guide for the EB lane to cut into the back. There should be one more 5/16" for a total of Qty. 12 5/16".
2) Many of the rings were 1 size to large IMO. Many were the correct fit and kept the rings in a proper tension with the rubber in straight lines between the posts.

(Continued, as apparently there's a character limit)
2) ...but some other rings were not in proper tension and looked like ovals when installed. The F and G were the biggest offenders (2" and 2.5" respectively) where the same O-ring is being applied to very different post distances, leaving some very loose and will kill ball momentum or risk damage to things behind if played in that state. Therefore I recommend if using this kit to purchase some extra 2" and 1-1/2" along with the extra 5/16 to ensure your Gorgar is properly protected.