Does the radio receive work? If so, then the BFO and the diode IC are OK, as it is used for both transmit and receive.
Since the problem started after making the modification for the AGC, can you undo that mod and see if the radio works?
I suspect that there is an error in the AGC modification that you made, as that is when the problem started. It would also help members in this group to know which AGC mod you installed.
I do not understand how the MAX9814 electret microphone amp is being used. That would normally not be wired to the VOL signals for the receive volume control. Are you using the electret amp as a preamp for the receive audio? The information that you are giving me is confusing. Is it possible to post pictures of the modifications that you made, or better yet sketches of the circuit schematic on how the modifications were installed? This for any and all modifications that you have made in the audio sections of the radio.
I would start with just the receiver, and get it working again before going on to the transmitter.