My suggestion is to pick up a 7/16" 8 point socket in 1/2" drive. That will grip those square head plugs (which you will also find on the gearbox and differential) far better than a crescent wrench or 12 point socket. And let you use a breaker bar (if necessary) for lots more torque than the special square wrench will give you.
I got mine at Sears some years ago, but when I tried to buy another one recently, the store I visited didn't have them. So I ordered one from Amazon.
On my own cars, I also swap out the square headed plugs for hex socket plugs that can be turned with an Allen wrench. For the drain plugs, I get the magnetic version. Both can be found at MMC for just a few dollars.