We normally instal a hyd switch/gate/ball valve lock off onto the hyd pressure feed line - with the valve open raise mast - then with hyd levers in neutral. close the valve - if it drifts down its the seals in the cylinder. if it stays up its normally a hyd control valve( Spool)
Safety tip -- relieve all hyd pressure before installing check valve - lower mast to ground - these machines will bite you....or kill you....
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