What oil is used in a 98 vw cabrio convertible top pump?

VW sells the oil at $25/quart. Another VW book I read said Dextron III Power Steering fluid is fine. If you have low oil and the top doesn't work look out for hose leaks and hydraulic cylinder leaks! Cylinders are behind panels next to rear seat. It's a closed system and should not become low.

By the way putting in the fluid is a drop at a time situation, a real pain in the ___