T&T: Velvet drive

[Henry Wing]

I'm in the process of changing the oil/fluid in my transmissions but I don't
know what's in there now. How can I tell?  I would like to use straight 30
weight oil same as the engines.  If it is trans. fluid in the transmissions,
can I just remove what I can through the dip stick hole and use the 30 wt
oil even though there may be a little trans fluid left in there?  If not,
how do I get all of the trans fluid out?
Henry Wing
Ft. Myers Yacht Basin