A few years ago I bought a Bogen 3063 mini-fluid head off of eBay. When it arrived, the little cast-in knobbly bit that holds the spring for the cam lever was gone. I don't know how these things break off, but it's not the first time I've seen it. Today, I finally got round to repairing it. Obviously, I couldn't put the broken cast piece back on -- even if I had it. So this is what I did:
I took the head completely apart. My plan was to drill a 3/32" hole just at the arc of the spring housing and insert a tension pin (or 'roll pin') into it. I drilled the hole too far away and the end of the spring kept snapping past the pin , so I ended up drilling a ⅛" hole, and used a ⅛" pin to hold the spring. Then I reassembled the head, putting in new silicon grease (the 'fluid'). The cam holds the plate securely, but I haven't put the head on a tripod or put a camera on it. But at this stage, the repair seems to be successful.