I pretty much despise silicone sealants, although I admit there are a very limited number of places where they work well.
For most gaskets I use Permatex #2, a very thin smearing on both sides, just enough that when installed it squeezes out a tinny tiny bit and you can see you used it, but not enough to squeeze out a blob that you'd then want to wipe off.
For valve cover gaskets I use contact cement, sold by Caterpillar as gasket adhesive and often called "cat glue". apply it to the cover and one side of the gasket, stick them together. Leave the head side dry, or some folks use a dab of grease, but the idea is to not have the gasket stick to the head, then valve adjustments are easy and the gasket is reusable for years and years.
I've used the copper gasket spray on head gaskets, and think it works OK but really don't have an opinion on it.
For the rubber seals on your oil pan around the main bearings I would use a dab of black RTV in the corners. Then permatex #2 for the side gaskets as mentioned.
Grigg
