I dont replace the panel.
I remove the trim around the wipers and scuttle cover, unbolt the master cylinder and move to one side, remove the brake servo.
Remove the throttle pedal and unbolt the pedal box.
The unbolt the leaky plate, you can then push it into the cabin by circa 20-30mm, clean it all up well with panel wipe or a good solvent.
Then apply a good polyurethane sealent around the edge of the lower half of the edge of the plate and bolt the plate back up, the sealent then oozes out and you can spread it across the remainder of the jointl to fully bridge the gap (its by now well sealed anyway).
Then refit said items.
I did the first one some 3-4 years ago, none have ever leaked since.
The fault with the plate is the seal/sealent used, the above method eratins the plate but fits a much more superior sealent (all be it a pain to use as its hard to remove from your clothes/skin)