> How would you recommend to prepare the board 2 pieces to ensure that
> the epoxy will penetrate and "grip" on/in the wood?
I'd use some coarse sand paper (24-36 grit if you have it) or a even a
rasp to grind back the wood fibers to a clean surface.
I know you don't want to remove the pieces from the W/M, but you must
make sure the surfaces are clean and free from any residual glue from
your previous attempt at repair.
Don't worry about removing more wood, you are after a clean and rough
surface, and the epoxy will replace it.