In looking at prices on eBay, etc, I notice that the Hasselblad 503CX goes for much less than the 503CW.
The only significant differences I know of are the winder capability and GMS. Are there other issues that are dragging down prices? I normally shoot wide and normal, so the GMS should affect much, right?
I love my 503cxi, which has TTL flash metering and will accept the external winder but does not have the gliding mirror. The mirror cutoff is barely perceptible with my 150mm Sonnar and completely imperceptible with any lens of shorter focal length. It's very pronounced with the 250mm Sonnar, but I haven't used that lens in at least 2 years. I'd get the CX if I were you. The only differences will be the winder capability and the mirror. If you don't care about either of those things, spend the difference on lenses.
I've never cared about the winder. Hasselblads are so well designed ergonomically that all the winder would give me is a heavier camera. I can shoot an entire roll in a few seconds without ever taking my eye off the prism finder. Why in the world would I need the winder?
Well the 503CX probably gets less because the 503CW is the current model and you have the 503CXi and 501CM models which are newer than the CX. If you don't need a winder and long lenses are not required, go for it and grab a bargain.