Keith Monks M9BA

Dunno but I had that arm under its original name and it was wonderful until I destoyed it.  If I still played vinyl, I'd make you an offer. 

https://www.stereophile.com/content/audio-design-m9ba-tonearm

The arm was famous for its mercury bath contacts. There is one, "new in box" unit for sale on the Bay which could give you a high water mark for pricing, but I suspect that, other than collectors and the old school Decca cartridge aficionados, there is a limited market for this arm. Cool artifact--if the mercury is still intact, you ought to check laws re sale of product containing same. Good luck,

I had one mounted on my Ariston RD11S turntable. It required frequent cleaning of the mercury contacts. It was difficult to keep the liquid silicone from contaminating the contacts causing drop outs. Otherwise it worked fine with my mc cartridges. I bought mine new for $150 back in 1978.

I got mine from John Wright, the designer, who was also the designer of the IMF transmission-line loudspeakers.   He also helped me build mine.