mixture, I don't know which 2 bit company you deal with, but mine doesn't 'buy time' it does an immediate line test. The things I mentioned are real, corrosion on contacts in plugs is not unusual even gold plated ones can suffer, filters can fail although rarely I've seen 3 examples that have gone o\c (not mine) I had a situation where if I was on line and the phone rang the connection would drop the BT engineer traced it eventually to a badly corroded connection on the pole.
As an electronics service engineer about half the faults on the sort of M\Cs I worked on could be cured by removing edge connectors cleaning them up and re-plugging, or lifting and re-plugging the EProms. It takes just a few seconds to check these things, and does no harm. People like yourself who always look for the most complicated reasons possible for any fault before checking the basics are liable to cause more harm than good. Most people if there is no power to a M\C would check that the power lead is plugged in, I presume you would take the Power Supply to bits.