It is not unheard of for technicians to disable the monitors and alarms in order to stop those pesky trip outs.
Years ago, I was aware of a Cat 2 ILS which didnt conform to Cat 1 standards whose monitors were disabled.
I also know of LLZ beams drifting by as much as 45 degrees in heavy rain. It was uncertain whether it was beam width or direction which was out of tolerance. Luckily the aircraft became visual at approx. 1000' agl.
The only way this can happen is if the monitors and alarms are disabled - otherwise there would have been a transmitter change and if this second transmitter was also out of tolerance, the LLZ and G/S would have shut down.
Likewise with G/S signals which have a tendency to drift with water table height. The temptation to disable the monitors and alarms in order to have a good nights sleep must be overwhelming.
From memory, it is an ICAO recomendation that ILS's are flight checked every 120 days. Of course with modern electronics this ferquency is ludicrous. Nevertheless, there are still ILS sites with 1970's vintage equipment who hardly ever do flight checks because of financial constraints.
It is at these locations where there is a liklihood of technical hanky panky. We are also fortunate that the weather is for the most part nearly always benign in these places.
I also wonder whether the present trend for flight checking on a commercial basis can lead to a compromise in standards.
Its been more than 12 years since I had first hand information - however, the sceptic in me has difficulty in accepting that things have got any better.