WW did not have a special compartment for their stuff, so you should be able to reference that set up at any large RV store and come up with the same one. Which o-ring are you talking about that you can't seat? The hardest part will be disconnecting the lines from the unit as they have a crimp ring on most, but you can replace that with a stainless hose clamp or buy a crimper. I had mine out to reroute the air vent line, and I can't recall it being too technical. Mine was a CL 4005, but the same compartment as you pictured.