Hope this helps others in the same spot. Looking very closely at the 2 burners not lighting up, it was easy to see that while the ignitors were sparking, the spark was very different that the 2 that worked. I turned off all the lights and watched them spark in the dark. The spark on the 2 that worked was brighter, stronger, and primarily sparking at the TOP of the ignitor. The 2 not working were sparking weaker, not as bright and very clearly NOT at the top of the ignitor. I ordered these 2 and replaced them and immediately it worked and all the ignitors now looked the same. Keep in mind that the ignitors replaced were not cracked but were showing "browning" and that indicates wear and tear and impacted the ability to generate a strong spark. Problem took as long to fix as it took me to replace a screw, maybe 7 minutes for 2 burners - piece of cake!