Check out my web page - there are some pictures of a cut-out valve that was made for the D14/D15 and probably the D17 as well (depending on series - I doubt it would work on a Series IV).
The cut-out or selector valve directs hydraulics to either the 3 point hitch/ remote cylinder or to the front end loader for the trip-bucket style. Yours is probably piped differently, but it may give you an idea.
On the Series I and II (and probably III) check the oil with the cylinders fully extended - you are looking for a minimum oil level in the reservoir. Be careful, though - too much oil and the extra will come out of the vent when you lower the loader.