Therefore, all the trappings of "GA" operations, ie: non reporting of defects, no money spent on aircraft, "ground tested OK" etc.
Unless the radar defect is accurately described by the pilot in the maintenance document, then the electronics people don't have much to go on in their diagnosis of the defect - if indeed there is a defect and not just the defective knowledge of the pilot on the limitations inherent with the operation of radar. For example, radar attenuation in heavy rain.
Pilots also need to read the POH for the radar in their aircraft. If the operator doesn't supply a radar POH, then search the internet - there is no shortage of excellent technical information for pilots on that subject.
Poor radome quality is a common cause of inefficient radar signals. Pin hole size damage, leaking seals and even incorrect paint repairs all serve to attenuate the radar signal. Typically, water gets into the honeycomb surface of the radome and then freezes at low temperatures common at high altitude. Radar cannot penetrate the thin ice layer on the inside of the radome and a thunderstorm cannot be "seen" until the aircraft is so close that a penetration may occur. On the ground the ice disappears and 'ground tested - serviceable` report is the usual result.