Rainwater Harvesting Pump Controller Problem

Our rainwater harvesting system uses a pump and that pump is controlled by a, well, controller. This has worked fine for years, but about six months ago it gave a fault and I had to press the reset button to get it going again. It then ran for several months, but about four weeks ago it tripped again, and then it tripped many times.

The controller is a controlmatic E, I believe and it has a PCB inside which performs all the functions. From the symptoms I thought it might be an electrolytic capacitor problem as the frequency of occurrance is increasing. I took the PCB out and tested the electrolytic capacitors and found that they were fine. I then took the power supply dropper capacitor out and tested that and it did not look fine. I replaced it with a parts bin capacitor and the controller ran for a few days with no faults. I bought some new capacitors as I didn't want to leave a parts bin component across he mains, even though it seemed to solve the problem. It was also slightly wrong in value. I put a new capacitor in the PCB when they arrived and the controller has run ever since with no faults.

I have a couple of videos about it here:

https://uk.rs-online.com/web/p/polypropylene-film-capacitors/1447774/

https://uk.rs-online.com/web/p/polypropylene-film-capacitors/8712613/