I used a synthetic DIII Castrol oil and I wish I hadn't, if only because I attribute that to my now pretty ocean going disaster of a transmission oil leak. I asked on the forum a few months ago if anyone knew of a more traditional, perhaps less aggressive and 'thin' ATF than that I'd used, but as I recall no one answered. So, not much help, but it'll be interesting to see if you get more of a response. Sticking to the adage of every cloud having a silver lining, the one plus to the bright red oil I use is that you can see where you've been, or parked, which means that you don't have any worries about it being engine oil.
JH