Hi there. Steve is correct. If you have the dreaded rust bubble, that's the tip of the iceberg. The rust has penetrated the metal and a bubble has formed under the paint. The paintwork is acting like a plastic bag with water under it. Two ways forward. Both really a body shop job. 1: get them to clean up the rust. Fill the the rust holes with body filler and paint. That will last for hours. 2: Cut out the rusty metal. Weld in new. Fill and paint and treat as best as you can with wax oils and sealers. That should a lot longer. Unfortunately these vehicle can suffer with this problem. Its a Merc.