nob,
I'm thinking you might have something similar to what is on my Cal21'. If you look at these swivel cam cleats from Harken one might look somewhat familiar. Note that the ones with the springs sticking up require your selection of a block to mount there.
Harkenstore Product Category
I'm presuming that the block and cleat in question mount on the starboard quarter gunwale of your boat. If on the mounting base it says F130 Austrailia you probably have the same block I have. I replaced it with one of the Harkens. You can size them up at a West Marine for what you need.
Welcome to sailnet. You've got one of the Cal's of enduring popularity. There's a thread here on a fellow who restored one and the pictures are phenomenal. You'll have to look for it, just check under Cal 20 in the archives. I'm sure it will be of help to you.