I found that the water was leaking from my tank, so I changed the rubber gasket which seals the nuts and bolts between the tank and the toilet base. When I tightened the bolts, I was cautious and hand tightened them to a snug fit, but I didn't tighten as tight as I could (fearing that I may crack the porcelain). Now there has been water slowly perspiring from one of the nuts. How hard can I tighten? Does anyone have any tips for sealing this water leak?

You were correct to be cautious about over tighten and breaking something. Hard to tell you how tight you can tighten the tank bolts.

I suggest turning off the water. Flush the toilet and hold the lever down until all the water has drained. Dip and sponge out any remaining water. Remove the tank bolt and dry the surrounding area. Pull the gasket down slightly from the head of the bolt. Put a bead of silicone between the gasket and the head of the bolt. Put a bead of silicone around the hole in the tank and reinstall the bolt.
With silicone between the bolt head and the gasket and between the gasket and the tank, minimum pressure should seal against any leak.
Tank should be firmly bolted to the bowl but there should be some slight movement when pushing back toward the wall.

My preferred way.
All toilets are not made the same. If there is enough room between the tank and the bowl for a nut to fit, or if the hole in the bowl is larger than the nut (usually is), you can remove the tank and put a nut on the bolt and tighten firmly to seal against a leak. Then reinstall the tank using the washer and another nut.

Sorry Harold, but the silicone method is simply not needed here! I install a whole lot of toilets as you can imagine and have never used silicone for the job. I do like your approach of using a nut and a metal washer to first tighten the bolt to the tank until the rubber washer in the tank spreads a bit and then installing the bolts through the toilet bowl and tightening the tank to bowl with another nut and metal washer leaving just a small bit of wiggle between tank and bowl when finished! In fact, most tank to bowl kits come with the extra nuts and washers for exactly this reason!

If I knew the model of toilet and the approximate age I could probably tell more here, but we'll have to see if FFB returns...

Mark

Mark, I agree that it is not necessary but it is an easy way for FFB to avoid the stress of tighten the tank bolts. He/she doesn't have a 159 years of experience like you and I.

(That is 59 years to me and 100 years to you.)