RV-9 Lower Cowling
 

I have a heat blister just below the Vetterman Exhaust Crossover. Should I remove the blister which is approximately 6" in Diameter and repair or leave it alone and apply Van's heat shield over it. The exterior is not damaged or blistered, just the roven-woven layer. This Nine has been flying two years. Why it blistered is beyond me. Any suggestions would be appreciated.
Gerry Chancey
RV-9, N92GC
J-3, NC88583