I have no idea how old my MB is. It is a 21HP and I have never seen one with this motor. Even though it still runs good the frame is rusting and the trim motor is almost rusted all the way through the case. The hours meter broke several years ago. I would estimate at least 15 years old??? The belt has never been changed or really much anything else. So my question is would it be worth it to get a new motor when the time comes or start over???

Longtail?

There should be a little plate on the front near the hour meter or choke on the frame with a serial number. Call mb with that number if you want to know year. As far as the rest, hard to say, as things may not be as bad or mat be worse than you've conveyed in your post. Take a few pics of the areas concerning you (trim, etc), post here for feedback, and take the kool-aid drinkers that tell you to get a gtr with a grain of salt (they're coming, I promise lol). It may be best to sell what you have for a reasonable price to someone wanting to undertake a project, or may be a new engine and trim and tach is all you need.