Ok old school mechanics. Does the seat spring in the pic supposed to have more pressure that a ball point pen ? It seems extremely weak. Seats are smooth . Looking through bore scope see no cupping or ridges from seat on valve bore. History: Chasing boom drift/ bleed off on a 743 History: Leak behind pump Weak lift / boom drop 15 sec from max to ground Replaced rusted lines between pump and shroud . Lift greatly increased Boom drop greatly slowed Tested cylinders: Left showed bypass Resealed both.. left was definitely bad. Boom lift increased a slight bit more. Boom drift slowed even more . Takes about 45 sec - 1 min. from max to ground. Have tested spool center - good Linkage adjustment-good What next ??
Found it... Port relief valve inner o-ring came apart. All good now.