Many floors aren't perfectly level, and many toilets aren't perfectly flat on their bottom (AS stuff, particularly). So, you don't have to be heavy at all if the toilet doesn't sit level, just the bolts will NOT prevent it from rocking and ANY rocking will break the seal. Wax gets squished, but it doesn't spring back if the toilet can move leaving a gap that can leak.
Remove the toilet, clean the wax off, set it in place without wax, verify that it doesn't rock, and if it does, add shims to make sure it can't, then set it down with the wax and you should be golden.
A toilet can leak from only a few places: around the flange, from a loose hose or connection to or in the tank, between the tank and the bowl, or from a defect (crack, hole, etc.).