Sencore SC3100 / Oscilloscope

[Jana617]

The trace would disappear after 15 min. Determined the problem in "High Voltage Board 1000". The Sencore replace a resistor with a MOV. Schematic shows it (was) as a 1 ohm 1 watt resister. Blowing cool air across it trace returns. I can not figure the marking on the MOV.....It states one side -XX72 X0XO other side GFCB China. I called Sencore. No help.