I don't know anything about the Raritan but... two tidbits:
-- rebuild kits are available for at least some Wilcox-Crittenden heads. I have a WC "Headmate" (model 1460), which I assume is original equipment, and I've been able to find rebuild kits and spare parts for it online.
https://www.marinesan.com/Headmate-Repair-Kit-p/37057.htm
http://www.downwindmarine.com/Wilcox-Crittenden-Headmate-Toilet-Service-Parts-p-91002266.html
-- I recently attended a seminar on heads and plumbing as part of a YC general meeting. The speaker (who runs the "MarineSan" company in Seattle) said there is an off-the-shelf pump available that matches the hole-pattern of the WC Headmate.... and is a much better pump. Might still require re-plumbing the hoses in and out of the pump, but if the bowl of your existing head is still viable, it might solve your problem without being a major uninstall/rebuild/replace project.
I don't recall the brand/model of that pump, but might be worth a call to MarineSan before you start pulling things apart. The guy's name is Clay Peil, he seemed very knowledgeable about what works and what doesn't.
MarineSan's numbers are
800-624-9111 / 206-633-1110
https://www.marinesan.com
(for anyone in the Seattle area, they're located next door to Fisheries down by Gasworks park...)
Bruce