High all

My chimney is a masonry chimney made of good quality white bricks
thoughout. At the top is a cement cap, maybe 6 inches think,where its
rounded over into the flue rain guards. That cement top is cracked on
one side, with a gap of maybe 1-2mm for about 1 foot. I was considering
just filling it with either silicone or regular caulking. And tips?
Metal strap required? Ignore it? It doesn't look like its about to
crumble or anything.

Thanks!

Dean