I can answer the size question, the Urethane O-rings are size 319. I looked them up on Amazon and they are available cheap, but I did not know what density/durometer (?) to order, so I got them from Jessem with $12 shipping on an $8 order.
I was tempted to get a bag of 25 for cheap on Amazon, but wasn't sure they were the right ones. Also felt their urethane rings would probably turn to goo in three years like the Jessem ones did, so the extras would do me no good.
Maybe someone with knowledge can clarify.
Useless O-ring info: I have three Kits of O-rings from various places. Two are from HF, one metric and one SAE. They are identical same numbers, just different color box. The other kit is from ?, and looks very similar. NONE of the kits have a size 319 in them.
Rick Potter
DIY journeyman,
FWW wannabe.
AKA Village Idiot.