I have next to my Russian- also an American brother with whom I
have daily correspondence (Don Griffith). His story you can probably
deny or confirm. The story is that people posted their in Japan bought
Koetsus direct to Garrott brothers for their ''retips''. Aka ''not rebuild''
or ''refreshment''.
I know for sure what the Garrott Bros did to Koetsu's. I sent them somewhere between 30-40 Koetsu's personally in the mid 80's.
The Garrott's tweaked Koetsu's were so good that we occasionally had customers request a "Garrott retip" for their brand new Koetsu.
Part of the reason was the micro scanner styli they installed.
However, this was only part of the story. With each retip the Garrotts went through each cartridge from stylus tip to pin outs. Any issues were tidied up. Production flaws fixed. Sometimes they reworked what they considered to be design flaws.
This is true of all cartridges the Garrots retipped. Every retip, repaired cartridge was fully tested in a live system before leaving their premises.
As far as Koetsu's go I can tell you Garrotts considered them the worst built cartridges in the world. For example with the stone bodied Koetsu's built by Sugano, the generator/cantilever/stylus assembly were held in by paper shims. We actually had a couple of Onyx Gold where the guts literally fell out of the cartridge body. The Garrott's would remove the paper shims and rework the mechanical integrity of the cartridge.
There were other internal mods they did, but they kept most of the details to themselves.
It was this attention to detail that their reputation for delivering cartridges better than new flourished - they were much more than your average modern retipper.
It is no coincidence that the three best cartridge rebuilders in my view - Garrotts, Van Den Hul and Andreoli - all produced their own range of superb cartridges.