how can i fix a coal bed for Robinson Willey Excelsior?

The corner, approx 3 inches has creacked and boken off my elderly mothers Excelsior matrix style coal bed, which has odd coals placed on top. The service engineer has said it is a 'danger' and left a catelogue and his tel number to fit a new fire. I am no expert but i find it hard to see a danger the 2 parts fit perfect together and there is no sign of deteriation on the back plate. Any way is there some kind of adhesive/morter than can be used to put her mind at ease please.

Or a spare part anywhere
GC partno 157707 Makers partno 994731 description Coal Bed

Many thanks