D-Ring Seals on lines out of valve bank

[225d Cat]

Hello!
I have hydraulic oil leaking from the lines on the top of the valve bank on the old 225D Cat excavator. I would say they are hard from the heat over the years. I have new ones now and plan to chane them all out. I assume that the valves are all closed and the only oil I will lose is what is in the lines. What I am wondering is will there be any valves that could be open and possibly let oil through the pump from the tank. Should I pump out the tank? Also, what should I do about air in the system after new seals are in? Just run it slow and work the air out?

Thanks!!

[Bob/Ont]

Yes drain the tank, change all of your filters, clean out debris from behind the screen in the main filter canister. Try to get a pump with a filter on it to put oil back in with if it,s good.
Replace every line seal and plug seal on both valves, would be a good time to reseal the main relief combiner and summing valve, it's all in one piece but be carefull taking it apart. Get everything back together right.
Later Bob