I don't know much about hydraulic drives, but I know of someone who does. He is not a member, but he lives very near me and is (as far as I know) working to get his patented idea implemented in pretty much everything. All the buzz about his "Hydristor" seems to have come and gone, as several of his press references have been taken down. You may want to contact him, he is willing to talk to people who email him.
Hydristor - Home Page