Victor UA-7082 Arm OR Micro Seiki MA505L ...? (both fit my existing alternate 270mm hole)

I owned a nice 505 too, but because I had no TT that could easily mount it, I eventually sold it without ever having used it. Beautiful craftsmanship for sure. My fallible recollection is that the CW stub extended straight out from the rear of the pivot at the same height as the arm wand but I certainly could be wrong. Anyway, Elliot owns one, so he can set me straight.

I did not need to mess with my friend's  MA-505 or 505L counterweight section

a thin gasket that could deteriorate is seen here

I took a defective Victor UA-7045 apart, measured, found a solution in Home Depot plumbing dept, gathered new and old info here in 2020

bad victor gasket discussion here

the Victor Gasket is a stepped design, the front portion is smaller diameter and is drawn inside the end of the forward tube, the rear portion is the same diameter as the tube and is seen separating the rear counterweight tube from the front main arm tube

the Victor Arms gasket definitely deteriorate, the one I bought seems to have been renewed, but until I take it apart, I cannot be sure. There is a brass piece within that prevents rotation while tightening, I will verify it's condition

many photos of victor gasket problem here

Yes, no one disputes that the Victor tonearm counterweights tend to sag over time.  Happens to the best of us. Chakster used to describe this problem as an indication the tonearm was ruined thereby.  You and several others were able to fix the problem. Good on you. I've got a bag of faucet washers, some of which are tapered when viewed in cross-section.  Perhaps I will give it a shot, though at present I have no use for my Victor UA7045. Maybe there's no Home Depot in Russia.

I found my measurements of the Victor concealed brass piece and measurements of the gasket I found at home depot

I will take the 7082 I just bought apart when I receive it, go again to Home Depot, find the part number, take pics, measure the inside diameter this time.

I'm looking for the part number of the washer in your diagram.  I don't see it.  Do you have the number?  If so, and if you would share the info, that would be great.