Get it fixed, now. If it happens during peak boating season, you'll lose prime time, or maybe more boat damage or sinking, with possible loss of people too!
Imagine if you i/o falls off, how big a hole is in the back of your boat?
Parts aren't too expensive, just google:
http://www.mercstuff.com/gimbalrings.htm
It's usually the labor added to the parts that adds up. Some times the part can be $15, but it takes $2,000 of labor to get to it and replace it. Hours at $100 per hour can add up fast.
We all hate surprises at launch time!
Good luck, let us know how this ends up.