After much engineering and testing, the Shell LA3624 is the only fluid ZF recommends. I wouldn't deviate - penny-wise pound foolish IMHO.
http://www.zf-group.com/am/pc/pt/ampcpt04.phtml
From ZF's website:
Q: What type of oil do I need to use in my ZF automatic transmission?
A: Each transmission needs a specific type of transmission fluid to operate properly. The use of incorrect transmission fluid may cause extensive damage to internal parts of the transmission and may bring the transmission right back to your shop. For a complete list of ZF recommended lubricants please refer to the lubrication list.
Q: Can I fill my 5HP30 transmission with ATF Dexron II instead of the oil specified? Why?
A: It is not recommended by ZF to use any lubricant other that those specified (see lubrication list). Use of any lubricant other than those specified by ZF may cause extensive damage to the clutch (friction) plates inside the transmission and the torque converter.
I bought a 20 liter container (Part #S671 090 149) from Transtar Industries - this is enough to do 2 changes. I paid about $10/liter (a much better deal than www.jie.com!)... They only sell to dealers/transmission shops, so just make up a name! Good luck!!
Transtar Industries, Inc.
Phone: (800) 359-3339 or (440) 232-5100
infodesk@transtarindustries.com
Bryan