EDIT: The step ring you've pictured in the first post is similar to mine, but mine is raw aluminum. Your's might be steel? I mistook your question to be about the deck-level ring system (based on post #10 above).
I have 1989 Vision 32 and that collar system at the deck is a two piece assembly on mine. Yours appears to be a single piece, is that right? What year is yours? I unstepped my mast for transport last spring, so it's pretty fresh in my mind and I have some pics and vids.
FWIW, here's how it works on mine. It's made up of two aluminum rings with a conical rubber mast partner wedged between. You can see the two rings here.
The outer ring is bolted through the deck and fastened with nuts and washers that are accessible behind a trim plate in the V-Berth ceiling.We never even loosened these outer bolts. That ring stays put.
The inner ring is bolted into tapped holes in the outer ring. Removing those bolts was easier than expected. They were SS into aluminum so I feared the worst. Some good soul had coated them well with anti-seize. Before removal, one of the riggers had the good sense to make index marks on the two rings in order to put it back in the exact orientation it came off. That way if the hole spacing isn't precisely even, we wouldn't be fighting to align bolts.
That outer ring's job is to compress a rubber cone that effectively serves as your mast partners. Once the bolts were out, we slid the outer ring up the mast and and tied it off to a halyard to get out of the way. You can see that and the loosened rubber cone here in a still from a video I took.
The trick is to get the ring out without damaging it. First, you need to remove a single 18" long bolt that goes through the bottom of the mast as and essentially pins it to a collar that sits on top of the keel. That's your step bolt. Easy to remove - harder to put back in (see below).
Once that step bolt was out, we took some mast weight off the step by lifting with the crane. Two separate operators on two separate cranes, hundreds of miles apart both estimated the mast weighs about 600 lbs. Neither had a load cell on their crane. I guess you develop a sense for these things.
You need to use a rubber mallet and some blocks/boards to knock the ring loose from below - hammering upward from the V-berth (fun!). Do this carefully so as not to damage that rubber ring! When we did this, the crane was lifting the whole boat by the mast. My boot stripe was a good two inches above its normal level in the water. Once the ring is loose, you're home free. The mast just lifts straight out of the deck. You can see here that the outer ring that's left behind has a conical seat that accepts the rubber ring. When the inner ring compresses the conical rubber partner, that rubber deforms downward and laterally, forming a snug wedge.
We did not remove the rubber cone for transport, so the outer aluminum ring was effectively captive. But you'll either need to remove the rubber cone or work your cracked collar up off the top of the mast. That likely means removing your goose neck and all cleats and halyards, steps, etc. Depending on the condition of the rubber partner, you might opt for the long route. If the rubber is dry and friable, I would leave it alone.
BTW: the hole that was left behind needed to be capped/covered for transport. The classic upside-down bucket trick wouldn't do it. But a 16" pizza pan and a tube of silicone formed a nice seal and a perfect fit! Cheap, too.
Finally, stepping the mast at the other end of our road haul was pretty easy. The only hard part was getting the step bolt lined up. No matter how much we tweaked and jostled with the crane, the hole tolerances where just too tight for the far end of the 18" bolt to pass through the mast and collar. The solution was to order a 5/8" bridge reamer from Grainger to slightly enlarge, and align the holes. I did that a couple of weeks after the step and delivery cruise (motor only) and it proved very easy.
Hope something in there is helpful, even though your's looks to be a little different.
