STW Massive

On the way home tonight on my Roadrat – pre-built by Cy and the gang last year – I thought my chain had slipped off but it hadn't. The hub is no longer engaging so the pedals go round and I stop then fall sideways. I believe it may be knackered, so am wondering what hub to replace it with. Any ideas? And while people may take the mickey I prefer it to be singlespeed; it has done wonders for my fitness this year.

TBH I guess I should have stripped it down a while ago but I'm all thumbs and afraid of ending up with a load of parts left over, so I have generally just kept it clean. I'm certain the bearings are dirty but there is no ratchet sound any more… (sob!).