I had to replace the front case on my 346XT last year, and it was pretty easy. If all you need to do is replace the LCD window, it's even easier.
KDPZ4B9811A - Display Window
RCUN4C0405Z - Window Foam Gasket
Call Uniden Parts at (800) 554-3988 and tell them those are the part #'s you need. When I ordered mine it was something like $1.12 for the window and 99 cents for the gasket, so naturally I ordered a few of each.
To replace it, you remove the front case (6 screws on the back of the scanner) then pop the LCD window out by pressing it from the outside. It's held on the case by thin double-sided tape/gasket. You might have to clean up the remnants of the glue, but then it's as simple as putting the new gasket on and pressing the new window into place.