MacGregorSailors.com

I was in the process of replacing my old rudder on my 1982 Mac 25 when I discovered severe (IMO) corrosion around the rudder mounting holes in the rudder castle . I'm wondering if there is a source for a new castle or can the holes somehow be patched? Thanks for any helpful input. Click on Pictures to see what I'm talking about.

Looks like galvanic corrosion of the aluminum from contact with the more noble stainless steel bolt. It is happening to my X rudder brackets also. Really should have a galvanic isolator kit on the fastener (non conducting tube and washers to prevent contact of SS to aluminum.
Not sure who sells the parts for your model maybe try powersailor or bluewater yachts or the factory. If you use the search button the contact info should appear from other posts, or someone that has ordered from those places might chime in. I've never ordered from them yet (other than the factory).