Good news, got the encoder working! I had a cold joint on IC5, the pad looked wet but the leg of the IC hadn't actually gotten any solder on it. Still stuck on the buttons on LeMEC L, the transistors are all the same type from what I can see (marked with 6G) and the BAT54s (marked with 5A). Is there a specific IC that handles the button presses for the whole LeMEC board? It's odd that it all works on the LeMEC R but none of the buttons function on the LeMEC L.