Skip, how's about a picture of the "broken" part?
Sounds like you are saying you have a 2007 style mast and the mast base (the part containing the big metal pin) has a broken retaining edge. This is possible but it's more likely that the pathetically thin, metal crapass mast retainer clip (found just inside the mast receiver cup) is broken, rusted or bent out of shape.
So check to see if it is engaging. Then rotate the mast to see if there are any broken edges on the mast itself. Either way, it can be repaired by a dealer.
If it's a slipped mast collar, as Bob suggests, you'll be able to slide the mast up and down at any point of rotation. (This happened to my mast and it was reglued. So far, so good).
Check out this tech note to see if it relates to your problems.
http://www.hobiecat.com/community/viewtopic.php?t=5958Yup, love those mirage drives. There's always a paddle too, if you need to go "Old School".