Is this my electrical short ?

I have it writen down someplace, so don't take my word for what I am about to write. But, my neighbor told me to cut the ( if I remember ) - black/LT green wire, than replace the fuse, and try the blinker. He say's if the rear light blinks fast, but doesn't blow the fuse, than that's the short. He suggested this, because the socket is in bad condition, and needs replacing anyway. The only thing that bothers me is, where do you get the gasket for the socket ? that's what failed, and let the water in, in the 1st place right ?