Killer
The XL uses a check valve arrangement to pressurize the oil tank. When your oil tank is full or at an angle where the incoming pressure line is covered with the bar oil, it can suck the oil back to the cylinder area.
Empty your oil tank & look for a little sinitered bronze cylinder that went into the tip of the pressure line. If the line has gotten soft you may need to replace it as well as the rubber check valve that goes on the little sinitered bronze cylinder.
Bill Walcott