There's a pump which boosts pressure to the cold circuit (taps, bog
etc) in our house when a tap is turned on.

About 1 time in 5, it won't spin, but just sit there humming. As I
suspected, the electric meter spins pretty quickly when it's stuck
like this!

The main plate on top says:
OSIP Electropompe Tpe VCB45/42
0.33Kw 220-240v 2.5a 8µF
Vc:450 Hz:50 IS.CL:F

Inside, there's a capacitor. It says:
Italfarad - 05/90 (date of manufacture, I'd guess)
RP-3 10040
µF: 10 ±5%b
450V~ DB HPFPU
400V~ DB HPFNT
------------------------------
500V 120/10
400V H250 25/85 360V


So, there it all is! Do capacitors fade over time? Anyway of testing
with yer standard £5 Maplin yellow multimeter?
Any ideas greatly appreciated. Thanks!