Bleeding the head is just to remove trapped air in your system, you'll know it's done once no more air bubbles comes out the bleeder port. Once the fan comes on, that usually tells me all of your cooling systems are operating as it should, ie; CTS, thermostat, relay, etc. I don't know of a spray for the outside and I doubt it would resolve your problem because an IM leak is usually the case of an uneven torque. Besides it'll look mickey-mouse if u apply some silicone on the outside anyways. This might be a bitch, but I'd suggest u remove the IM and there's a copper gasket spray in a copper can that I love to use that u can spray on the gasket real good and it's very sticky. It's always does wonders for me. I think 3M makes it and u can purchase that at Kragen or Pep Boys. Good luck!!! BTW, are u doing this while we're writing?