Hi Pekka
Good to read from you and thank you very much for your detailed answer 
So I would definitaly paint the area semi gloss black after further careful cleaning, except the bolts and nuts, especially the nice brass nuts!
Best Regards to Finnland 
Lukas
Welcome back, David!
Are these all metal crimped lock nuts available new anymore? I was about to post on this very subject, and then I read this thread!
I made an unsuccessful attempt to remove the idler on my 120 for inspection, but was thwarted by the fact that I had no way of holding the head of the shorter bolt from turning, with the radiator still in the car. I worked out that I need a deep 9/16" AF ring spanner, so have ordered one. I noticed these unusual lock nuts whilst I was immersed in this job.
There are other all-metal lock nut designs, often used in high heat applications, which I might have to resort to. There’s something about a Nyloc that just doesn’t look right in this situation!
I’ve noticed some up and down movement at the outer end of the steering idler arm, but can’t yet determine if it’s due to a worn bush/shaft or the arm turning on the taper due to a seized idler. I suspect the latter, but won’t know until I get it off.