Welcome to the new and improved Proflex / K2 Tech Forum!
Welcome Dug,your 4000 is the same as the one I've been riding the last 9 yrs,I love mine and I'm sure you'll enjoy yours
Man-o-man, have I caught the bug bad! - early model has ODS (and had elastomers), the later model has Noleens front and rear with coil springs- early model has no gusset/reinforcement where the downtube meets the headtube (on the underside), the later model does- early model has "Factory Test" text where seat tube meets top tube, later model has something like "World Class Design"There may be other differences. ............even the original "Girvin" crank (rebranded Sugino) ..............all for $275 - Doug :-)