twodzusfitting....Attached is the correspondence I received from Mack Boring regarding the the transmission fluid for the Hurth transmission in my 1983 O'Day with the 5416 Universal engine.
Hello George,
Most major brands still offer Dextron III. Dextron III is available and is more commonly known as ATF fluid. In regards to Dextron IV this is a synthetic based fluid and is not recommended by ZF as viable fluid to use in their transmissions. ZF DOES NOT recommend the use of a synthetic based fluid in the transmission.
Thank you for contacting Mack Boring and Parts Company.
Happy Boating
Hello George,
I searched on AutoZone’s website. I am very surprised you could not find it at your local AutoZone. Here is a picture of the bottle they commonly carry and a link to their website. Most major companies are switching to different names for DEX III this is the way AutoZone has it listed DEX/MERC .This is a Dextron Mercon blend and will work fine for your application most DEX III fluids are a multi-blend with Mercon.
I also searched NAPA auto. They have the same DEX/MERC blend and commonly known as ATF fluid for NAPA it’s the same fluid named differently. I hope this helps you
I hope you find these fluids in your local auto parts retail outlets if you have any problems please feel free to contact us at anytime and we will do our best to answer your questions.
AutoZone - System Error
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NO_75200_0274140289