i dont know anything about heated seats before i start.
But i presume its the same principle as a toaster..... over time it wears out, dont get as hot as easy.
You COULD sell the seats on ebay, and then buy some more of the same, that might work better IF yours are worn out, which they might not be.
As said, i know nothing about how they work, but i reckon they could just be used, and the elements or whatever they use are worn.
Thats my penny :S