I DO NOT SUPPLY
As with other soundboxes, in addition to replacing gaskets it is often the case that a new insulator between the tonearm and the soundbox is required. This page relates how I replaced the insulator on my Decca 3 as well as making one or two observation regarding refurbishing the Decca/Meltrope 3. (As the Decca is the same as the Meltrope 3 the sizes and instructions apply to that soundbox as well.) I believe the similarity between the two soundboxes is due to the purchase of the Meltrope company after World War 2.
Decca (Meltrope) No. 3
The refurbishment of the Decca 3 is fairly straightforward when it comes to replacing gaskets as it uses the standard 2mm diameter tubing readily available on the internet. However a word of warning. The stylus pivot system is based on the positioning of 4 small ball bearings that become loose when the front cover is removed. 2 are placed below the plate on the needlebar and 2 on top of it. The latter 2 will almost certainly remain attached to the front cover and will fall off and be lost without you even realizing they were there in the first place. So, remove the cover carefully and be aware of the bearings. Secondly there is a thin washer housed in the scew on collar at the back of the soundbox. Take care that this is also not lost.
The insulator for the soundbox I made from layers of washers made up from 2mm and 3mm rubber sheet using a "Circlescribe", the device used for cutting circles for the components of the "Expanda" record albums. These things really are wealth worth obtaining as they can cut a range of circles useful in gramophone restoration. The dimensions are shown in the photographs opposite. Do not glue the components of the insulator together. I found this to be unnecessary. Also notice the inner most washer is slightly narrower on its inner circle. This is to form a separation between the inner surface of the soundbox and the end of the tonearm, a feature not on the original insulator. In addition the outer ring is slightly larger to allow a better fit within the collar.
Should the diaphragm be damaged it is very difficult to affect a repair as the needlebar is held to it by a rivet although I have managed to do it on one Decca 3 I repaired.