What I would do:

Cut a few inches of the old wire off until you get to good wire. You will be able to tell how far that is because the color of the wire strands will look like clean copper rather than the corroded stuff at the end. Once you get to good clean wire, see if the length is still enough to reach the solenoid. If it is you can put on a ring terminal using a crimp tool and attach it and be done. If it isn't long enough then I would solder splice a piece of wire to the old one to lengthen it. Cover this splice with heat shrink tubing and then crimp the ring terminal to the end of the new piece of wire.

 

i used a ring terminal in heat shrink tubing, and that worked out fine, turns out the battery was at half charge. but i figure i might as well get a new starter. mine is stock.

 

It's a common fix.
ignor the rest of the gobbeldy goop in the pic