is the head just not working, leaking, bowl broken? I have the same head in my 356 and during one of our cruises the toilet base assembly became cracked which started leaking. I also looked at replacement like you did with similar results. I researched online and found that all the necessary parts and maintenance kits are readily available at a huge savings versus total replacement cost. I removed the head and in just a few hours completely rebuilt it as good as new. http://www.raritaneng.com/products/toilets/manual/ph_2.html
Hope this helps!”