The clunking noise coming from the rudder is likely play between the pintles and gudgeons. You’ll need flanged sleeve bearings (aka shoulder bushings) for the gudgeons to address that. Washers help reduce friction where the gudgeons take the weight of the rudder - but wont help with the clunking.
The type of bearings you need will likely depend on your current arrangement - whether there are existing worn bearings - or none. It sounds like SLM build practices changed over time. If you have no existing bearings, you may need to get the gudgeons machined to make room for the bearing - as the existing wear may be too thin for any off-the-shelf bearing - and the wear may not be circular.
I have not done this project myself on my boat. I need to. I would use acetal/delrin, and buy spares at the same time.
Cheers - Jeremy
@bil has a previous post with a couple pictures (below):
We had some similar ‘thunking’ and upon hauling found some play caused by wear on the bottom pintle/gudgeon. Cymba had no liners or sleeves.
After doing research, we did not use nylon or delrin since it appears they may swell a tiny amount if continuously immersed in water (don’t recall exactly where I found that info) and I was worried about binding.
We measured the pintle diameter and inner diameter of the gudgeon and found the right size oil impregnated bronze bushings on McMaster Carr:
Install was just pressing them in by hand and the rudder has been great since.
On a similar, but different note, we also noticed the washers were very worn and replaced those at the same time with these:
Probably a little overkill, but they’ve also worked well so we’ve been happy with the results.