Read post #3 ----
if the unit has never been cleaned after 40 years of Lord knows what inside it,
it is advisable to do do it right, you are leaning toward Hytran which is an expensive lube with just as good, lesser expensive substitutes lubes avail. why would you want to put big $$ into a toilet/cesspool?
Purchase lesser expensive, but quality hydraulic oil and spend the saved $$ on a cub, Deer, wix or equivalent filter and gasket and clean up the cesspool in the reservoir.
Disclamer:
if the hydraulic fluid has been changed regularly then a drain/filter and refill is ok.
Just my .02 cents
