[gjbingham]

It doesn't look too significant to me. I think I'd leave it alone. Your cladding should bond everything together on the outside.

I think that cracks are a natural result of thermal expansion/contraction of the bricks during heating/cooling. Any uneveness in the application of heat across the dome (ie: top of dome getting the early heat first) causes stresses as the warmer spots expand faster than the cooler areas (my own hypothesis). My guess is that if you repair the crack as you describe, you're probably going to get it back again in the same spot or develop one somewhere else.

Who knows Jim? The repair might be worth a try. I doubt it will hurt.