M_Boats: M-17 Centerboard stuck

Dave, It's my understanding that both marinas used some sort of chemical solution and just beat the heck out of it from the side of the keel to try to loosen it up. I spoke with a fella at Montgomery boats and he suggested prying a metal rod into the top until you can work through it. The only other suggestion was to go in through the hull...sounds like a $3500 fix! It has been like that for a good 15 years I would imagine. It sat in my sisters yard in Tx until I picked it up a couple years ago. Any suggestions a good chemical solution to use? Someone else suggested liquid wrench. We've been sailing in light winds and we're ok. Just not able to get into anything too exciting! Carol B