Thanks to the forum I just completed my rebuild of my lift pump.
Just sharing an enhanced pic and somewhat blurry closeup of the location of small o-ring mentioned in previous posts, along with a couple of sources for them.
I used a dental pick to remove the old o-ring and installed the new one using a chop stick
as I didn't want to nick or damage the new o-ring using a metal tool. I can say I did notice a difference an increase in the feel (or drag) of the shaft when the new one was installed - glad I did it while I was rebuilding the valves.
I have about 80 extra o-rings...if you would like a couple (two!), PM me with an address, I'll send them to you for free while they last. Peachparts can source the rebuild kit for the valves.