Which hydraulic fluid for Cabriolet?

[yambrovich]

I have a 1993 300CE cabriolet (A124). On Friday, while stopped in HOT weather (98F) in traffic, I decided I'd had enough of my rotisserie chicken imitation and went to put the top up. I was on a slight incline to the left (driver's side lower than passenger side) and the top wouldn't raise!!! YIKES!!
After a couple of attempts, I decided to forget it and just drive home while continuing my slow roast. On the remaining 25 minute drive, my brain kicked into overdrive about the reason the top wouldn't raise.
Today, I pulled out my trusty Mercedes Benz E-Class Owner's Bible (Bentley Publishers - a GREAT reference book) and found that there's a hydraulic reservoir for the top mechanism. After pulling the carpet and trunk liner out to get to the pump / reservoir, I see that the hydraulic fluid is just above the MIN mark.

HERE'S THE QUESTION - WHAT FLUID DO I USE??? The Mercedes Benz E-Class Owner's Bible says to use MB Part no. 000 989 91 03 which I don't happen to have any of laying around in my garage. Being hydraulic fluid, do I just use DOT4 brake fluid (same as in the car)? OH PLEASE LEARNED ONES, your direction is requested. Does one of the techs have the answer? I DO NOT WANT TO MESS THINGS UP SO THAT I END UP HAVING TO PURGE AND BLEED THE ENTIRE SYSTEM.

Thanks all, I really appreciate the help.