No part number that I know off. It's probably Delrin, you can measure and try to find the size, or have a machinist make one out of a Delrin plug.
This has come up before. Here;s one post, there may be more: https://ericsonyachts.org/ie/threads/tighten-the-rudder.1488/
Also, check the top bearing. Remove the cockpit deck plate, turn the rudder hard while sailing, and see if the rudder post wobbles. If so the top deck bearing assembly may be loose, which is just a matter of tightening the four bolts.
Interesting. Okay I will check it out this weekend when I get to the boat. I hadn't heard or noticed anything weird under sail, but when I initially had it hauled out the surveyor noted a little play. Maybe I'll get lucky this weekend and resolve it when I swap my house batteries out. I really appreciate the help!The top bearing is sneaky, or at least it outfoxed me.
The whole underdeck assembly is held in place by the bolts in the plate at lower left in photo. If the bolts become loose, the bearing collar hidden beneath the deck slides around and you can hear the rudder clunk every tack.
However, and here's the sneaky part, the deck plate gives no sign anything's wrong. One simple test is to turn the bolts (machine screws) with a screwdriver. If they turn easily, the nuts on the other end are loose.
It's hard to reach the little nuts under the deck, and they are not in the line of sight of any routine inspection, which is why they're worth checking if rudder issues arise.
View attachment 32804
It sounds like if I do have to replace the bearing I might as well do that too?Sounds like you are (project wise) beyond just lubing it up, but over the years a number of owners here have found some satisfaction in thoroughly lubing the shaft thru the often-ignored zerks (grease fittings) on the rudder post tube. These are often challenging to locate. They are also often ignored by a succession of owners.