I normally use 10W/40 in my mini , but have used motul 20w/50 the last few changes. The 20W/50 is less prone to cooking especially now my bike is minus an oil cooler. I've had no problems with my clutch slipping at all and it shifts and runs no worries with 20W/40. No reliability issues at all , its doing a great job. So far ive tested out Motul , silkolene , Mobile , motorex , belray and yamalube oils so far all 10W/40 (besides the mineral oil used on run in) in both my grey lifan 124's and 140's. The 20W/50 so far goes the longest without cooking and does the job on par with the 10W/40. I didnt rate silkloene , cooked the oil in 2 rides. Had a bit of clutch slipping too even when it was warm
Preety keen to try some Torco oil next , all the factory mini teams seem to be running that...