You learned the hard way like I did. However it was after I hooked up the camper in Florida on a Saturday night after midnight traveling from home in Chicago. I thought I had appropriately winterized the toilet however if I had read the manual I would have know to take it out for the winter. Found a guy in Orlando that sold me the part for $50 on Sunday morning. This is from page 9 of my toilet manual for winterization.....
Toilet warranty does not cover freeze-damaged water valve
The Dometic 310 and 320 series toilet warranty expressly excludes coverage for any damages to the toilet or vehicle that may occur as a result of improper winterization of the toilet. An indicator of improper winterization is freeze damage to the water valve which results in leaks. Dometic 310 and 320 series toilet water valves exceed maximum water pressure as defined by
North American plumbing code agencies. However, if trapped water freezes in piping that supplies water to the toilet, it expands and creates extremely high
pressure that can damage the valve (see photo). To avoid this, winterize the toilet as described in this manual. If freeze-damage occurs as a result of
improper winterization, replace the water valve with a 300/310/320 toilet water valve kit, part number 385311641. IF WATER VALVE IS RETURNED FOR
WARRANTY CLAIM, DOMETIC RESERVES THE RIGHT TO DENY CLAIM IF PROBLEM IS CAUSED BY FREEZE DAMAGE.
See this link page 9 for the image
A – Freeze Damage Indicator Window: white stress marks indicate freeze damage
B – Water valve damage due to severe exposure to below-freezing temperature