Good question. Thermador doesn’t even offer the 27″ size anymore. Due to its age, there are no longer parts, and places to rebuild the panels have become almost nonexistent. I think even if fixed, you will be running into newer problems down the road. I would look at the GE profile or Cafe lineup as they make many 27″ ovens that fit almost all existing cutouts. These ovens feature so much new technology like air fry and built-in recipe centers I think you will find these useful. I know you have a dimension issue, but sooner or later, you need to address it. Now is the time.

GE sure fit link: https://www.geappliances.com/ge/ge-appliances-fit-guarantee.htm 

You definitely can just take extra care when moving it around. Cast iron can scratch the top if it is moving a lot. Make sure you clean the surface immediately after cooking as cast iron reside can leave marks on the glass top if left to sit too long after cooling down. I would suggest heating the pan at the same time as the top, meaning turning the burner on with the pan in place. Many of my customers love to cook with cast iron and have done so on glass tops for many years with no problems.

They come pretty standard to fit in a 30″ opening, and height can vary about 1″ depending on the brand. You would want to make sure you have an outlet in the cabinet above as they all plugin today and are not hard-wired. I would make sure proper venting is in place if not recirculating. Options include today a convection mode on select units. So the micro can double as an oven if needed. So the first thing to check is space, 2nd is the venting requirements, then you get into specific features. LG, for instance, has a model with an easy-clean interior and a pull-out visor to give more venting space and a higher cfm motor. It is a unique piece that works very well as a hood, not just a microwave!

LG extend a vent 2.0 link to LG page