Wood breaks down at 500° F and vapors containing 50% to 60% of the heat value are released by 1100° F. After the gases burn off and moisture is evaporated, charcoal remains and burns at a temperature exceeding 1100° F.
The stove gasket sealant in the picture has a maximum operating temperature of 900 °F. I believe this would work because of my experience with a similar problem. I had an emergency one day and needed to fix several broken firebricks. I used the red kind of high temperature gasket sealant, for engines. This was two yeas ago and this has been holding up very well. The red gasket sealant generally has a maximum operating temperature of 600 - 650 °F. After a bit of research, I see that the copper kind (of RTV sealant) seems to have a sometimes higher or lower maxiumum. I found one kind of copper sealant with a maximum of 700 °F.
But my advice would be to try the 900 °F sealant, specifically for stoves. You will need to clean the surface as well as possible (maybe use a spray bottle to rinse the area with water) before applying it.