Dave in Indiana,
If the centerboard won't come down, I guess you will have to remove the  
centerboard cap and find out why. ( On the trailer of course) Must be something  
jammed in their with it, like mud or a fish or......?
Mean Green is a great cleaner, but I don't believe it will remove the rust.  
I'm not sure what will remove the rust without destroying the Dacron the sails 
 are made from. Hopefully someone else on the list can help.
 
Rummy