Were you getting leaks from the control valve? I will be doing the same in my 763 which has a leak from its control valve. Generally I don't worry too much about getting dirt in as I am going to disassemble totally and rebuild. I clean parts with diesel and/or degrease with lye first. Rusted parts get submerged in a solution of lye, washing soda or baking soda and water and connected to a battery charger for electrolysis. Final cleaning of castings is usually by pressure washer. Once cleaned I simply drop part in diesel and let the water seperate. During assembly I use generous amounts of hydraulic oil and then tape up or cap inlets. After a brushdown with paint thinner and the part dries I paint it. Last but not least, I install it on the machine. My 863 is still all apart so every piece gets cleaned, rebuilt and painted seperately. Once assembled it's like new.