Just saw this. I used to fix and restore 80s arcade games and cabinets. A lot were made with MDF and painted, and often got water damage (like when a restaurant mopped the floor right against the cabinet). You have a laminate veneer, so no need to worry about paint. I don't know if you can disassemble the cabinet so you're only working with the damaged side. If not, it'll be harder but not impossible. Of course, if you can disassemble the cabinet AND remove all of the veneer easily, it would be easiest just to have a new piece cut at the proper thickness and put the veneer on it. First, you'll need to get access to the swollen MDF by removing the veneer without breaking it. Might need a heat gun to soften the adhesive, and a putty knife to gently work the veneer up. You probably won't be able to match it if it breaks, so you'll either have to redo the entire piece with new matching veneer or play puzzle master trying to put it all back together and hope it doesn't look worse than it does now. After it's off, you need to treat all of the swollen area with Wood Hardener (see the pic below). You can get this at Home Depot or Lowes. Treat the swollen area per the instructions and let it dry. Once the wood is nice and hard (that's what she said) use an orbital sander to sand it smooth back to the original shape. If there is any pitting or missing chunks that you're worried about, you can use Bondo (wood/metal) to fill and sand. Now, wipe all the dust off and glue the veneer pack on. If you can't disassemble the cabinet, you'll have to sand it by hand. Wrap a ruler in sandpaper to get in the tight spots.