It’s really good to know I’m not the only one using Castrol R! And really interesting to hear your replies, so I’ll try to answer as many (or perhaps the few) replies to this topic.
Captain Pugwash, I’ve heard about these problems quite a lot. I use Castrol R40 all the time and with regard to settling in the petrol tank I think there may be something in it. I rode my scooter (S2 TV175 engine) around this morning and there was frost on the grass and on windscreens. The old girl did seem to smoke a bit more than usual at first so perhaps the oil was starting to settle at the bottom of the tank. Time will tell on this score because I shall be riding her around whatever the weather.
Apparently the R30 that you ran yours on is still available in Oz where they use it in colder weather. To my knowledge it is no longer available here in the UK but I managed to get my hands on a couple of litres a few years ago (for £5 each on a second hand stall) so may switch to this for a while when it gets colder still and see what happens.
I have run mine on R40 for years and I’ll leave it up to everyone else to decide what they think of my decision as I start to make my replies. I do think ratio is very important and I have tried 50:1; 40:1; 33:1 and 25:1.
I’ve had no problem with sticky rings or anything of that nature but I have read of the “glaze” that it leaves on engine components. When I did a complete engine strip-down recently I found it’s true that everything had a shiny glaze left on them. My opinion is this isn’t in itself harmful and could be why so many racers used Castrol R because it prevents seizures. I used to race a TV 200 with a GP200 engine (home-tuned cast iron barrel) in the cutdown class and the engine ran brilliantly. I’ll upload some photos of the engine so everyone can make comments and say what they think. And yep, I agree with you Captain, it smells great

Hope the pic ain't too small to see but this is the extent of carbon build up after running the engine for years on a mixture of Castrol R40, plain modern mineral, part-synth, fully-synth, and sometimes a mixture of one, or more than one other of the aforementioned. Despite what they say about Castrol R not mixing with other oils I believe this to be a misunderstanding. On four-strokes where people use Castrol R in their crankcases I can see why they wouldn't mix, and this is where the warnings come in; but on the total-loss, burn the whole damn lot in the combustion chamber two-stroke, it seems not to matter.

And this pic of the cylinder head is after cleaning and starting afresh. Next year I'll strip her down again to see what condition the engine components are in after having run her exclusively on R30/40. The pics of other engine parts which I've yet to upload, but will get round to during this debate I'm trying to get going, will shock some, and horrify others. By the end of it I hope a whole lot more people will have something to say on the subject!