REL Q400E hum: what caps to use?

Bought a old REL Q400E, first use I noticed a tiny hum in the driver but didn't take much notice until a few weeks after use it annoyed me, so I popped the backplate off, all seemed ok but the last main electrolytic capacitor was all buldged on top.

So it'll need replacing, but I think it's best to do all 4 at the same time.

Any thoughts on replacements?