A manufacturer that punches out several parts from a single sheet of steel was having a problem with oil occasionally spraying out from between two hydraulic valve sandwich modules. They would disassemble the D03 valve stack and find one of the O-rings completely gone.
The valve stack had been taken apart several times over the last three years, and only new O-rings were installed. Viton 95-durometer O-rings were used because they have a Shore durometer slightly higher than 70.
The press ran four years without a failure, and no one remembered the reason for the first failure. Typically, a missing O-ring is a sign of high vacuum, but the circuit compensated for this with a module from Sun Hydraulics containing an anti-cavitation check valve. They unscrewed the anti-cavity check cartridge and found it to be working well.