My experience has been to only use silly cone when you come to corners with gaskets ,
The right stuff is close to what the manufactures use when assembling eng. & not using gaskets , it holds on almost to good , bend sheet metal covers when removing , then clean up is the most labor intensive , also the bits & pieces go everywhere .
If you leave about 4 - 6 bolts in , but out about 3 turns , then tap on cover from side to get the seal to break free , the best to reuse a gasket is permatex gasket sealer & brush on .