Hydraulic Fluid is based on Crawler Track Lube.
Press Release Summary:

Original Press Release:
X-1R Biodegradable Hydraulic Fluid
Designed specifically for equipment that operates in environmentally sensitive areas, X-1R Biodegradable Synthetic Hydraulic Fluid is made with non-aromatic, biodegradable base stocks and specialized non-toxic additives. It is ideally suited for equipment where incidental contact of the hydraulic fluid and the environment is possible. The unique synthetic formulation of X-1R's biodegradable synthetic hydraulic fluid provides equipment with superior wear protection and lubrication. It is a direct spin off of the Crawler Track Lube for which X-1R was inducted in the Space Technology Hall of Fame and earned the designation "Certified Space Technology."