The tail light arrived today but It is a reproduction unit not new old stock as I had hoped. Still I can't be too fussy. At least I now have one
The box is marked "Intaza Motorcycle Replacement Taillights & Lenses". I've never heard of them but the quality looks ok. There are no markings on the lens though if you are after originality.
I've also discovered that the hand made alloy rear tail light frame on my IOM model has cracked from vibration. So if you have an IOM model it's worth checking the tail light mount. It might just be ready to fall off!