Sewer Gas Odor in Bathroom

We’ve been in our home for about 4 years. A couple of years ago, we began to notice an intermittent sewer gas smell in the bathroom on the ground floor. It seems to coincide with strong winds. We are assuming that the vent pipe is cracked, but don’t know how to go about repairing it. The other side of the wall which houses the vent pipe is a closet – and there’s no smell at all in such a confined space. We’ve tried sealing all the gaps around pipes and electrical outlets coming through the bathroom wall, but the smell persists. We replaced the toilet and found that the old one did not make full contact with the wax ring. So we installed the new one with two wax rings stacked to make sure we had a good seal – but the smell continues. The bottom half of the wall is tiled, as is the floor. There are no gaps visible where they meet, and no baseboard to obstruct the view. Any other ideas?