Permatex's Ultra Copper Maximum Temperature RTV 101BR offers the highest temperature rating in the industry: -75F to +700 degrees intermittent. It is three times more oil resistant than any silicone out there. So good, in fact, you can use it on exhaust manifolds. Permatex High-Temp Red RTV 26B silicone sealer has the next highest temperature rating of most silicone sealers, -65F to +650 degrees F intermittent. It delivers outstanding service when used properly. Use High-Temp Red at gasket gaps, such as where oil pan side rail gaskets meet rubber end gaskets. Use it sparingly because, when it oozes out, all you're doing is wasting sealer and it looks unsightly.
When it comes to areas like wet jacket bolt threads and paper gaskets, the old standby--Permatex Form-A-Gasket--tends to be your best friend. You'll recall that wonderful smelling brown stuff from working on your first car. Form-A-Gasket #1 is fast drying and permanent. Form-A-Gasket #2 is slow drying and non-hardening, which makes it possible to disassemble quickly if necessary.
Light-duty gasket applications like valve covers and oil pan side rails can get by with yellow Edelbrock Gasgacinch #9300 in a can. Spread a thin film of this stuff on gasket surfaces for good sealing and adhesion. Gasgacinch holds gaskets firmly in place. It is not a gap sealer, but instead a gasket glue.