It was exactly the part I needed.
SeaLand/Dometic 385236096 Spring Cartridge Kit.
Fits all SeaLand / Dometic foot pedal VacuFlush Marine Toilets and Traveler Toilets except the Eco Vac Models 140, Model 210, Model 510H and 5000 Series Toilets.
Ordered this on the weekend and received it on Tuesday. It is exactly the part I needed. It took less than a half hour to install. I just needed an 8mm socket and a Philips screwdriver. I am told there is a black cartridge and a white one like this one. They are different. Make sure to check the one you are replacing with your toilet model number.
I originally went to an rv store. They gave me wrong part #s. When I questioned them on it they found they were out of stock. These guys got me right part numbers got the parts out right away with 2 day shipping I got parts on sat of labor day weekend. These guys rock.
This spring cartridge was an exact replacement for the ten-year-old cartridge in which the spring had broken from metal fatigue. It fit perfectly, and was simple to install.
ARDEMCO shipped part to incorrect address but noted error on their own, called me to notify me of the error and immediately sent second part to me. Received it promptly. Installed it and it fit & functioned perfectly. Great customer service!