Just to reignite this age old debate, 2t Self mix according to the MSDS is a mineral based additive. I have extracted a little info from that document. im about to put it in my GUIII 3.0l DI.

Material Safety Data Sheet
1 .
Identification of the material and supplier
Castrol 2T Selfmix
Product name
462220
SDS no.
Product use
Lubricant for two-stroke engines.
For specific application advice see appropriate Technical Data Sheet or consult our company
representative.
BP Australia Pty Ltd (ABN 53 004 085 616)
717 Bourke Street
Docklands VIC 3008
Australia
Tel: +61 (03) 9268 4111
Fax: +61 (03) 9268 3321
Supplier
+61 2801 44558 (or 1800 14 14 74 within Australia)
EMERGENCY TELEPHONE
NUMBER
Product code
462220-AU07
Hazards identification
2 .
NON-HAZARDOUS SUBSTANCE. NON-DANGEROUS GOODS.
Statement of
hazardous/dangerous nature
Composition/information on ingredients
3 .
Highly refined base oil (IP 346 DMSO extract < 3%). Proprietary performance additives.
This product does not contain any hazardous ingredients at or above regulated thresholds