You can use the stock motor if you choose. It's held onto the regualtor with 3 bolts. I'd just keep the stock motor as a spare and use the one that comes already attached to the new regulator. Once you do these enough you can get one in and done in about 20 min start to finish, lol... Yea, they tend to break often.

BTW, lube the felt window guides w/ some greasless dry lube really well. These windows like to stick to the felt and it can cause the regulator to do exactly what you see now. Even if it doesn't "feel" like its sticking it probably is just a bit.