What year are the bikes that this is occurring on? I have worn out my first seat cover and bought a replacement from an inmate here. Seat pan looks fine so far. Noticed I'd lost a rubber bumper last week.
I had 2 pans crack badly on my crf' 450x bikes (they all used to do that) and also managed to rip open a pan around the mounting screw (on an KTm exc) when my boot got caught during a pretty wild enduro. In that instance I later fixed the pan by getting some plastic glue from a hardware shop, using the entire tube to impregnate a few layers of loose weave fleece material. Reason I went with that as are re enforcement is that it's made from polypropylene. Plus I didn't have anything else handy...but it seemed to work great and held up for a few years until I on sold the bike. Might be worth a try if the dealer pleads innocence.