I have a 70 in which I changed the tilt cylinders and went to start it up and got the fault code of 524251-1. So went to office and it was looked up as a 5V (OORsomething?) Pulled the trany dip stick and the oil was foamed, like fluffy foamed. But it was doing the same thing as in no backwards and forwards. On the top of the trany are the words "Hydro only" so I dumped in about half a gallon and was backing out the lift when it quit again, this time the fluid was less foamy but still had air in it.
In my case I am changing the filter and filling with JD40 as I think the iso fluid is not the one to use.
Funny thing is, is that this lift was used for days with no problem traveling and then I fix the tilt drift and poof there it sits.