"Hyster" is long gone...now Allied Systems. You can download parts and service manuals for free from this website. The D6 uses the D6N or D6C model but don't get your hopes up for finding much in the way of parts for these old units. I have had pretty good luck locating used stuff out of the Pacific Northwest (logging country)
At the Allied site click on Allied Winch then parts manuals of which there is a two page listing.