Unfortunately the MDC is a solid glued in piece the only way to dismantle it is to "break" it so to speak. Especially the diaphragm area it's leaking from. You have two choices. Forget about it, if you have perfect pass the boat will run fine without it, or buy new one.
The MDC just went up from the old 299-300 range to 600. Medallion allegedly only builds them to order now I was told so they they upped the price being it's a special piece nowadays. I called around to several dealers and was able to find one still marked at the old price. I do know waterskis.com/midwest mastercraft has them in stock but they have already marked them up to the new price.
CURRENT: 2008 SANTE 210
2000 Mastercraft Xstar
2004,2005 Ski Centurion Avalanche C4
2003, Ski Centurion Cyclone
99,2000,2001, 2002 Ski Centurion Elite V/Hurricane/lightning
88 2001 Nautique