Yep, open it up(but first mark where the cases come together with a scribe, so it can be re-assembled the same way).
If the starter won’t turn over, one of several things has happened; The starter motor has seized due to brushes binding up, lack of lubrication in the bushings of the motor, the battery is weak , the engine has seized or it could be a combination of any of the above. A website for starter motors is:
