A large entertainment stage is rotated by a Geroler type hydraulic motor shown on the circuit. The regenerative center position on the directional valve eliminated a sudden jerk when first started since both ports were already pressurized. The pilot operated directional valve also had a smaller pilot pressure orifice installed to slow down the shifting speed softening the acceleration phase of the start cycle.
The problem they were complaining about was the big puddle of oil leaking out from under the stage every couple of months that required replacing the hydraulic motors that were leaking out through the shaft seal. They changed to a different Geroler brand motor and still suffered the same failure.
A large number, more that 50% would be my guess, of all Geroler type motor do not use a case drain. Typically, the output port of the motors goes back to tank with little back pressure. The case drainage leaks into this low-pressure port and keeps the case pressure at a low level greatly reducing the wear on the shaft seals. The regenerative spool and meter out flow controls require an external case drain since both ports see high pressure at the same time.