I just emailed Castrol trying to find out which of their ATF’s are synthetic blend so I though I would post the response here in case anyone cares:
Thank you for contacting Castrol North America.
Castrol always recommends following the guidelines of the original engine manufacturer for the recommended fluid for use in your specific application. This information can be found in the vehicles owner’s manual or by contacting the manufacturer directly.
Castrol ATF+4 is a full synthetic transmission fluid.
Castrol Dexron VI ATF is a part synthetic transmission fluid.
Both Castrol Import Multi-Vehicle ATF and the Castrol Dex/Merc Domestic Multi-Veh ATF are conventional.
Thank you again for contacing Castrol.
Castrol Consumer Relations