Those Rifa caps in the line filter are safety caps. I was told this is generally a failure mode of safety caps. Short voltage spikes on the power line damage the caps. Safety caps are self healing. But with every damage they lose a bit of capacity. When the capacity reaches a critical level, the line filter may start oscillating at its resonance frequency. This effect in combination with the parasitic resistance will heat up the capacitor and destroy it finally.
Thats why it is also not a good idea placing a second line filter in front of an existing line filter. The combination might get also resonant and destroy al least one of the elements.
My opinion:
If the scope is not in daily use and is unplugged most of the time, new Rifa caps will last very long again. Maybe the scope should be kept in a dry room too for various reasons.
Regards,
Gerrit
