You may find the thread below helpful, especially since you mentioned leaking around the handle.

In addition to the tips in the thread, examine your gasket carefully and try reversing it. Sometimes a gasket will work in one direction and not the other.

Carol

Here is a link that might be useful: Leaking Mirro Pressure Canner

Also try applying a VERY light coating of oil on the gasket (just the outer part, no need to get it down into the groove), wipe it off and see if it helps. Sometimes at the first of the season I need to do this. It moistens the gasket just a bit so it is flexible enough to conform the the shape it needs to.

Deanna

My Mirro that I use for cooking, not canning, with the lid lock mechanism has begun to occasionally not seal where lock meets lid...

This was all I've found, and has worked so far but I wonder if that isn't kind of a dumb design, think I would find it frustrating if mine were a size for canned goods rather than something I cook in just a few times a year.

"If steam continues to leak around the lid at the site of one of the handles of a Mirro canner that has a lid lock mechanism under the handles, it is because the lid lock mechanism has not seated itself completely. You may be able to remedy this by gently shaking or moving the canner from side to side. If that fails, you will need to let the pressure return to zero naturally, open the canner and jiggle the lid lock mechanism and dry the area around the mechanism."