You can do this. Words, words, words, it’s not that hard, or precise.
prior link to good photos
https://www.audiovintage.fr/leforum/viewtopic.php?t=55306
You take it apart, remove the old rubber, install the new stepped rubber gasket (dimensions below), reassemble, no critical adjustments.
The hardest part is having/acquiring the tiny allen wrench to fit the 3 allen head set screws. That’s the only tool needed.
1. Disassembly:
A. Remove the rear counterweight shaft/assembly.
a1. loosen set screw on the counterweight shaft (probably on the bottom).
a2. unscrew the entire counterweight assembly. (counter clockwise from rear). It has internal threads, it simply spins off. Fear not, keep turning.
****Visible Now: old rubber on brass piece inside short chrome piece****
B. Remove the short chrome tube extending out of the rear of the pivot
b1. loosen two tiny allen-head set screws on the bottom of the pivot.
b2. pull short chrome piece out. (brass piece probably held in place by old rubber)
C. Remove all old rubber, pushing brass piece out of the short chrome piece.
***Notice: front of brass piece has tabs. front of short chrome tube has notches.***
Tabs in notches keeps the brass piece from spinning during re-assembly.
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2. Size of ’Stepped’ Rubber Gasket!
You need to take rear of arm apart to fix it, so take the short chrome piece and brass piece with you when going to the plumbing store/dept.
Described horizontally, facing cartridge.
2a. Front portion that becomes invisible when pushed onto the brass piece and inside the short chrome tube: 9mm outside diameter x 4mm long. (mine started out longer than 4mm and was cut by hand to 4mm long) (doesn’t have to be perfect length or perfect cut).
2b. Rear portion that remains visible, (ends up looking like a simple washer): 13mm outside diameter x 4mm long. (it could be a bit larger diameter but would visually exceed the counterweight tube’s diameter). (it could be only 3mm long. (Not more than 4mm long, you don’t want this portion of rubber to allow too much sag when re-assembled.
2c. inside diameter of gasket: sadly I forgot to measure it. it slides onto the brass piece. anyone know the diameter of the brass piece ___________ ? Take the brass piece with you.
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3. Re-Assembly
3a. insert brass piece into the short chrome tube.
3b. locate brass tabs in the tube’s notches
3c. push rubber gasket onto the brass piece inside the short chrome piece
You want the brass tabs to stay firmly in the notches before proceeding.
3d. Insert short chrome tube into the hole in the rear of the pivot.
***How far into the pivot?***
Far enough for the set screws to lock it in place, not too far to contact/interfere with arm/pivot movement.
3e. Tighten the two set screws. lightly snug, check full pivot motion, tighten firmly.
3f. Spin the counterweight assembly onto the brass threaded shaft.
*** Pull rearward while spinning on. Do not push the brass piece forward when doing this, you want the internal brass tabs to remain in the chrome tube’s notches so the brass piece cannot spin.
3g. Firmly snug the counterweight shaft to the rear face of the rubber gasket.
*** Now the counterweight has pulled everything together, has tightened the brass tabs into the notches, is holding itself firmly against the gasket***
3h. tighten the set screw preventing counterweight shaft movement.
Done.