I never used silicone sealant, that I'm sure of, but I have done the grease method before only to have the gasket "slide out" over time and start to leak. Using that same gasket that was sliding out, I switched to Aviation sealant and it has solved the leak problem. Now I use the Aviation sealant only for valve cover gaskets and used it on my leaking Dana 300 two years ago to seal up the splines at the yokes and rear shim plates for the front bearing preload cover. The synthetic oil was creeping out of the smallest of openings on the D300 and the aviation sealant cured that problem too. The aviation sealant is a lot easier to clean up when one needs to put on a new gasket too. It remains tacky and can be removed with Mineral Spirits for prepping the surface again for a new gasket if needed.
I'm on my fourth valve cover gasket since the engine was rebuilt. First was removed to change Valve cover color from wrinkle back to blue powder coat and I used the grease method only to have it start to leak which led to changing gasket with new and aviation sealant. Second time was a for loose baffle plate under the cover that needed to be secured before falling into the valve train. Third and fourth time was taking care of the internal coolant leak.
The grease method for sealing a gasket works well as long as you have bolts or nuts that don't come loose that hold the valve cover down. That was one of my problems too and have cured it with these little gems called Wedge Lock Washers that are two piece and prevent bolts from backing out. They have another name but I can't remember and are very popular on header bolts as well.
1984 CJ-7 Renegade