Upon arrival found system low on charge. Performed leak check. Found oil stains around service valve. Used IR leak detector and found heavy leakage around the high side service valve. Replaced core and found seal damaged. Once new core is installed performed second leak check. Found nothing. Added 8LBS of R410A. Charged system to proper sub cooling. Temperature split is @ 20. Indoor temperature is dropping. Unit is operational upon departure. Recommend adding surge protection and getting back onto service plan.