I have a hand full of 3/8 drive snap-on allen wrench sockets from my provious life, but have a hard time justifying the cost to buy any more just to use two times a year. I needed a good quality 14 mm allen wrnech to remove rear end differential plugs, so I was really surprized when the MAC dealer suggested an alternative. He sells individual or sets of allen wrench insets that fit into a 7/16 socket. I have looked in Autozone and NAPA for a 14MM allen wrench or allen socket with no luck. If you have a tight plug, good tools are essential to remove these things. There are a lot of internal wrenching bolts on an MB, so if you don't already have a good set of these types of tools, I recommend them as a very good quality and economical alternative for a DIYer. The 14 mm unit cost around $10. I did not price the whole set, since I have the other common sizes already.
Lefty loosy, righty tighty!