The Houdaille shocks used glycerine diluted 10% with ethanol. For ethanol, use "denatured alcohol" available at hardware and paint stores. You might find glycerine at the drug store. The seals in the shocks are not compatible with oils. You can buy the correct pre-mixed fluid direct from such lever shock rebuilders as Apple Hydraulics, Five Points, or M&S Hydraulics. See http://www.antiqueshockabsorbers.com/parts.asp for a pint of fluid. You can use the denatured alcohol to flush the old fluid out. It's about the only safe solvent to use that will dissolve old glycerine, though it's flammable. If you fill the shock with alcohol through the plug and it leaks out around the shaft, then the shocks need rebuilding.