Frank,

I think that was a full-synthetic oil that had limited distribution and is now discontinued. Nothing magical. I may be wrong.

Dave

Correct....It was/is a full synthetic gear oil used by some in New Zealand and Europe for model engines. No personal experience as I've never seen it in the US. For some reason Castrol chose not to actively market "Model Engine" oils in the US but were heavily involved in Europe. 99% of the synthetic oils used for "model engine" two strokes in the US were/are manufactured by Dupont/Dow Corning with some formulated for private labeled companies and generally only sold direct in Large quantities (think multiple drums). Motul markets "Micro 2T" in the US as well as Europe but it's pretty pricy and contrary to popular belief (and their marketing hype about all their other oils) is not Ester based. Primarily because pure Ester based synthetics don't mix well with Methanol

From sunny New Zealand

Castrol MSSR suddenly became very popular for a short time, easy clean up and well priced compared to castor, my memory of it was my worn old motors (poor junior modeler)  quickly became more worn as the synthetic removed the varnish from the castor.

It fell out of favor, I use castor minimum 10% in every thing now

You are very lucky it wasn't sold in the USA. It was used during the castor oil shortage in the 70s. Many good motors were wrecked as it broke down rather easily