Lacking a leaded capacitor in that general range, carefully touch a wire from the top of your new C50 to the I/O trace while in receive mode. This bypasses the new board. If it restores audio then you know if the rest of the receiver is still functioning. In that case, check the gate of Q3 to ensure that it is getting the RX voltage. If it is, then either Q3 is bad, R2 or R4 is shorted, Q2 is shorted, or some unimaginable other combination of bad things.
Looking at the top of a 2N7002, with the single pin (that's the drain) away from you, the left pin is the gate, the right pin is the source.
If there is no audio when you couple the audio past that gate then we can assume that your replacement capacitor is bad or that the receiver chose that moment to quit.
Having a little outboard audio amplifier would provide you with an excellent tool. Just a good blocking capacitor on the input will allow you to probe from product detector to speaker.