This is all paraphrased straight out of my Velvet Drive Service
"Check the oil
after the transmission
has been running and is at operating termperature. Shut down the engine
with the shift lever in neutral and immediately check the oil level.
Use Dexron Type F (ATF) or any hydraulic fluid which meets the C-3 oil specification.
Change oil if operating temperatures have exceeded 190 deg.. Change once every 1000 hours or annually.
If your engine
never reaches 3000 rpm
you can use a high quality 30 weight oil but never mix different oils or fluid in the trans."
Hope this helps.