What to add to hydraulic reservoir behind Radiator

[Zimectrin]

Need to top off the hydraulic reservoir that is below the surge tank behind the radiator on my Freightliner.

Label says "Dexron III or equivalent" which I understand was standard in 2002.

Now it is 2010. Web research tells me Dexron III is no longer supported and has been replaced by Dexron VI, but still see Dexron III for sale.

Does it make any difference?

Any comments are appreciated.

[Gary RVRoamer]

Dexron VI is supposed to be compatible with Dexron III, but if you can find a Dexron III-equivalent you can certainly use that too.

[Cruzer]

The one exception would be is there was a service campaign for your coach. Freighliner had a number of cases where the 400 ISLs would overheat in the side radiator XC chassis. My 2004 Bus had one of these recalls and part of the campaign was to replace the Dexron hydraulic fluid with good old 15W-40 engine oil. They're reasoning was that the Dexron thinned out and didn't allow full RPMs on the hydraulic fan motor when hot. If your coach was part of that SC then I'd run 15W-40 instead of Dexron. In not, stick with the Dexron.