I don't know -- I'm going to have to respectfully disagree and say that if you can find a replacement case, go for it. Now, I'm saying this after completely disassembling my T2 to see about fixing the screen buzz problem, and I'm also the type of person not afraid to take things apart. It's not that complicated for the T2, so I'd imagine it would be similar if not identical to the T3. On a scale from 1 to 10 (with 10 being the most difficult), I'd rank it a 5 or 6.
Incidentally, I decided NOT to do a hardware based screen buzz fix, and just registered Lightspeed -- buzz free now! But it was worth taking my T2 apart to investigate the possibilities. After reassembling it, I have to say that the slide works better than ever. At least I now know I can easily replace the battery, screen, motherboard, case, etc., myself if needed in the future.
Anyway, back to the original question -- the problem is finding a T3 case. The Get High Tech website doesn't have them and they cannot get them (I emailed). I was thinking about buying a "blemished" T3 from Palm for $229 and then just replacing the damaged casing with a nice, clean $10 casing, but no dice!