[wingnut60]

I still think any type of brand-name ATF is suitable for this application. There is no temperature aspect to degrade the fluid, and generally, no way for contaminants to enter the system (condensation can always form in the fluid resevoir). If contamination were a hazard in this system, we would be told to replace the fluid at certain intervals, or there would be a filter to change. If the brand of the fluid was important, it would be addressed in the manual with dire warnings cancelling the warranty (similar to the Ford/GM/Allison transmission recommendations).
And full synthetic should always be better than conventional ATF, especially if operated in areas of low temperatures.
Joe