I don't remember it being a 10MM. I thought that it was about a 5MM or 6MM allen, but it's been a year or so since I changed one. It is a challenge to reach in there but it can be done. It seems as if I used just a plain old fashioned L shape allen and some time, but I can't remember for sure. I may have used an allen socket and ratchet.

With that kind of job it just takes persistence, patience, a good variety of tools and an occasional foul word to get 'er done. Even with it where it is, it is easier to change than many TXV's that I've seen.

Good luck,