In Reply to: Re: 601 oil leakage from hydraulic sump to transmission posted by Richard NY 2N on May 28, 2018 at 15:42:56:
New replacement pressure tubes for both four speed (NCA-945B) and five speed (NDA-945B) transmissions are available. Fairly simple repair - pull the old one out and drive the the new one in. Requires splitting the tractor. I have no experince with the aftermarket replacements but here is one source - 4th and 5th items on the page.
Replacement Hydraulic Tubes