Probably tighten the bolts a little bit and you will be fine.
Chances are that the gasket compressed over time, and now you need to tighten it by 2-3 turns. Don't over do it. You only need them snug, not tight as you can get. I would say about 20 foot pounds of pressure, or what I would get out of a nut driver.
I think they are either 1/2" or 9/16" bolt heads. Either 5/16" or 3/8" bolt threads, so they will break if overtight. And you want to "Compress" not flatten out the gasket. With proper compression, the gasket will need to be compressed about every 3 years, until it is around 25 years old, then replace the poor thing.
Good luck!
Fred.