I had a problem with the fuse board early on.
Some fuses were not passing current even though the contacts on the board were clean & bright as were the fuses, which tested good. I sprayed the board contacts with contact cleaner, & replaced the fuses. All working, well for about 8 months, when the problem returned.
This time I used a microfibre cloth & contact cleaner, & gave everything a good rub.
That was over 10 years ago, & the problem has not returned.