[len47merc]

Having recently been through this and ultimately biting the bullet and rebuilding all my shocks I can tell you that ALL of the rebuilders I spoke with use 30 wt hydraulic oil to refill the shocks after rebuilding. The original fluid in mine had turned to a dark-greenish, viscous paste that neither hydraulic oil nor castor oil will mix with or break down. Before sending the shocks out for rebuild I attempted flushing them and refilling with hydraulic oil and realized some improvement. For grins one shock was sent out for rebuild and I could not believe the improvement over the remaining three. It's worth the try but if your shocks have never been rebuilt or cleaned-out and refilled with whatever material you plan on refilling them with the likelihood is high that the fluids will not mix well and the true effectiveness of your shocks will not be realized. Good luck!