Decades since I refurbished a Rayburn and that was a total strip down and
rebuild.
However I would suggest that you replace all the fire bricks and if you
get any out intact regard them as a bonus as future spares.
If they are like normal solid fuel burners the fire bricks should come out
relatively easily (for various values of easily) because they were
probably shipped separately and installed when the stove was commissioned.
An installation manual for your stove would probably give fitting
instructions.
Have you got one/ asked Rayburn for one/ Googled for one?
Cheers
Dave R