There are two factors which govern tuned (anti-resonance) counterweights.
Primarily, when a weight is suspended (spring leaf) from the (counterweight
) shaft, it will vibrate out of phase to the rest of the arm thus cancelling most of the vibrations.
Secondly, everything has a resonance frequency (think of opera singer and wineglass). The self-resonance frequency of a tonearm with cartridge can be further diminished if we tune the suspension system for the actual weight. In the case of the early anti-resonator weights (701 721) they were set for one or two predefined frequencies. The obvious problem here is that we use different carts with different weights, thus the dead-weight changes and therefore the calculation for the resonance frequency is off.
The later units (741 and a few others) had extra client adjustable anti-resonators which allowed for ULM or standard 1/2" (different weight) carts to be brought into the proper resonance/anti-resonance range by means of calculating the deadweight of the cartridge with hardware against compliance.
This is the most effective way to go, and if you can find one of those you hit the jackpot.
A bit of background.
Nothing could make an engineering team developing a tonearm more happy than specifying a single weight/style/contour cartridge for the arm. With that, the complete arm can be designed from the get-go to work withing the resonance envelope, minimize the counter-"weight" /travel/ adjustments, remove head-shell and simplify anti-skate force adjustments. This is perfectly seen from the earliest B&O arm ST1 also used by a very special PE 3210 in the 1950ies:
(look at entry 11).
Later on the Concorde design Ortofon line and today the still practiced P mount system goes in that direction.
tried to go the same way with the TKS and ULM designs, but needed to cater to all the other Cart manufacturers as well, hence the technical overburden required in the arm design.
Coming back to the defective weight in question, once a tuned resonator is opened and "adjusted", it may perhaps no longer droop, which is by itself an improvement over having the actual weight touching the frame/shaft), the resonance tuning will be lost. The tuning process is out of the scope of DIY unfortunately!
--and I have the set as well---