After a week of waiting and waiting for the parts to arrive from Lazydays that was (allegedly) shipped overnight, it seems our Dometic SeaLand Concerto toilet was no closer to getting back in service quickly.
A call to the parts people in Tampa found me talking with someone very helpful. They told me the part number 385310964 they ordered for me would be here monday. That number did not have a familiar ring to it. A search through Dometic's site showed that part fits a model 3309 toilet. We have a model 3210, however.
Here's what we did to repair the Dometic:
Our new THETFORD was aquired for under $200 from a local RV dealer. It was cheaper in the long run than dealing with the hassles of warranty service from our dealer.
Life is "comfort"able again!