The Talking Machine Forum — For All Antique Phonographs & Recordings

I just tried, and with just one turn of (teflon) tape around the aluminium sleeve, the soundbox wouldn't go all the way back on the tonearm, so any air leaks must be very minimal.
To get a better look, I unscrewed the forward section of the tonearm (for the first time in 20 yrs) with the intentions of smeering a bit of silicone or even vasoline in the throat of the soundbox to make a perfect seal, but then I got to thinking about the now crumbling 4 white rubber buttons along the edge of the aluminium sleeve.

These obviously serve no purpose in sealing the join properly between the tonearm & soundbox, so the only reason I can see for them to be there, is to apply light pressure between the two pieces, so as to keep the prongs of the bayonet fitting seated in the slots properly.
Vasoline, teflon tape & even silicone, I doubt would do an efficent job in applying the same pressure, so my solution was to cut the buttons off flush with the surface of the aluminium, and to simply insert a soft rubber washer of the correct size into the throat of the soundbox
The rubber washer now serves the dual purpose of applying light pressure between the two components, and it has now made a completely airtight seal as well.
No messing with tape or sticky silicone, and the soundbox can still be easily removed as it was originally.
I had noticed in the last year or so, the reproducer had developed a very slight rattle now and then on certain notes, which had me wondering if it needed adjusting or even to be rebuilt again, but I discovered the buzz was actually caused by a couple small hard pieces of the white rubber buttons which had fallen inside the soundbox.
Thankfully the buzz is now gone, and shouldn't reoccure now the perishing rubber has been removed, & the machine sounds fantastic once again.
While I cant say I've noticed any improvement in bass responce etc (though I've only played 2 records since installing the washer), I must say I feel better knowing the old rubber buttons are gone, there's no empty space around the buttons in the throat of the soundbox, and the seal is now completely airtight.
It kind of makes me wonder why they bothered incorporating the buttons into the design in the first place, when to me, a washer seems a much easier & effective way to go.

A very elegant solution! And one that the maker should have included in the original design, as you say. I performed a somewhat similar mod on my Exhibition: between the back flange and the body of the sound box, where others have used a smear of vaseline as a sealant, I installed a large felt washer. This positions the sound box, and hence the diaphragm, a fraction further away from the gooseneck, and that stand-off seems to improve the overall response. (The washer came in a washer assortment I picked up at Horror Fright a/k/a Harbor Freight, and it happened to be just the right size outer diameter as well as center hole for the purpose.)

Ahah! My set-up no longer has the 4 rubber buttons. I can see witness marks where they once were but didn't know about their existance. Yes, the thin washer you made should be perfect. Thanks!