I have a couple of spares knocking around. I opened them up and they are different again! The PCB is neither green nor blue, but maroon -- and all the components are very helpfully labelled part with numbers and values, as on yours.
One of the 8-pin chips should be marked NE555. Orient the chip so that the bar is at the top, and count the pins from the top left (1) to the bottom left (4) and back up the other side from the bottom right (5) to the top right (8). There might be a dot next to pin 1. The timing capacitor should be connected to pin 1 on one end (ground) and pins 2 and 6 on the other end. Some of the connections may be visible on the PCB, some may be underneath the chip and not visible.
On that basis it looks very much like C4 as you say, which has the same value that mine did (0.1uF), so swapping it for 47uF or 100uF should get you in the ballpark. Good luck!