There is a steel sprocket.
It still amazes me that MMC keep things so close to their chests - unless maybe they're just too disorganised to know what's going on in the shed next door... I had a belt and sprocket replaced under warranty last month (and what seems to have been a 'real' warranty fix, ie: one I didn't need to pay for, unlike the Centa, but that's another story of course....) and I specifically asked if my very helpful dealer could ask MMC about the Steel Sprocket rumours I'd seen on here. "No", said MMC to their enquiries, "there is no such thing". So I had another self-destructing version fitted, which may or may not last more than the 5,500 miles of the original.
All very frustrating, I must say. I'd so love to be able to have a "TM Members and MMC owners meeting" one day, just to talk over all these things and to get their side of the story. There must be more to things than we get to see on this side of the owners/factory fence!