The large amount of heat from the 12BH7 suggests it is indeed conducting a lot of current, which is consistent with the measured voltages. If the R1 is correct and the LEDs are lit (meaning R2A and R2B are correct) the I worry the transistors (the large ones, MJE5731A) may be reversed, or have a solder bridge at their connections.
Here's a test, if you can't find anything along the lines either of us Pauls have suggested: Unsolder the black wire at D3, leaving it connected to kreg on the board. Put your meter (use clipleads!) between D3 and the black wire, and set it for 200mADC to measure the actual current. If it reads 23.5mA then the C4S is good; if it reads a lot more then the C4S is delivering way too much current, and something on the board is either mis-wired, fried, or has a bad solder joint. (Or, as is always possible, there is something else I have not thought of that's gone wrong!) This one is a puzzler.
