Personally, I'd either replace the strip of veneer across the whole panel as shown above the white line in the picture below, but I would attempt to replace the section above the blue line first.
Unless you can find some mahogany with an almost perfectly matching grain, it's near impossible to patch veneer straight across the grain without it standing out like dogs things

Cutting diagonally across the grain as shown by the blue line will be far less noticable, but replacing the top strip should make an invisible repair.
That said, it might be worth looking closely at the interior of the cabinet, under the motor board & in the horn compartment. I've been lucky on a couple occasions where I've found more or less book matched veneers on the interior, and have made an invisible repair by removing it from the inside where it cant be seen. At least that way, it's aged the same as the outer veneer (new veneer tends to be a completely different colour), and often has at least some original stain or/& finish which is very helpful when trying to match the patch to the original outer finish.