We had the same thing happen to our 2001 Adventurer. Keep in mind the 200 lbs. is on a lever about 3' long when the stairs are extended, so there is a fair amount of stress on the 4 mounting bolts. Also keep in mind you're constantly carrying heavy loads when you pack for a trip, go grocery shopping and, return home and unpack. Another step killer is using one of those stair support posts and forgetting to fold it up before retracting the stairs.
As I mentioned the stairs will come off easily they're held in place by only 4 bolts. On ours I removed the stairs, measured the size of the plate they are attached to and made another one from 7 gauge steel. I drilled the appropriate holes to allow the stair mounting bolts to protrude through. Before installing the reinforcing plate I welded up the cracks in the original plate. The whole project took a morning.
If you need to take it to a shop remove the steps first and have all the measurements. It should take the shop a couple hours or less to weld up the cracks and install a reinforcement plate. Around here welding shop rates are currently about $50.00 per hour. The plate will cost between $25.00 and $40.00. So for less than $150.00 you should be able to get a mounting plate better than new
