Orange Crush 20RT Mono Amp humming

Looking foe some friendly advice 

I have some knowledge repair small electronics
my neighbor bout over a used Orange Crush 20 RT Amp

soon as you power it on with Nothing connected it "HUMS" he asked me if I could take a look at it for him as a favor..

so, I took the Lid off and looking inside and under a Bright light, I see slight water damage on the Main PCB Edge.

Also on closer inspection, it also looks line the TDK 2025 This is the main power amp component (U9 Dual mono Amp) that's Bolted to the heatsink, and looks like it has been replaced at some point in the passed...

I suspect due to the slight water Damage the Humming is coming from the TDK2050 as an
Open Short and Allowing power to go to the speaker as a HUM.

Also on the main board, C4 marked as 104J100 needs to be replaced

but I don't have the Schematic or Component list, but need to know the Value of C4 and what type of Capacitor it is...
any help...
Thank you in Advanced.