Looking for a little power trim help

I have a 1990 merc 115 and the power trim started to make a almost grinding sound when I would bring it up or down. It only took a few try’s and it got slower and slower. Not it only makes that sound and will not move. Could there be a gear that is stripped or is the trim motor going out. Any ideas. And does it take much to change the trim motor. Thanks.

http://www.boats.net/parts/search/Merc2/Mercury/parts.html
Start there. They will have a schematic breakdown of the trim.
I would have found it but dont know which motor you had on the list.