Early 1981. It is among the first C made, and extremely rare, but only the early 5, 6, & 7C sell for high prices. I've been scanning eBay auctions for vintage C, and they're not nearly as common as vintage D, and their auctions don't last long. C's don't sit. I think modders may prefer C because of 26mm diameter Li-ion cells. 32mm diameter cells don't provide any more capacity, so even D hotwires will use 26mm cells with a sleeve. No sleeve necessary with C. I could be wrong about that, but it makes sense to me.