We had a heck of a time finding the strong mouse smell in our 8520. Turns out they had climbed up the rear wiper blade, found a tiny hole to get in between the cab ceiling and the top roof panel. There, they built a nest. But the worst part was a few of them leaped to their death down the air inlet pipe from roof down to the cab filter. We used a lot of lysol and febreeze on that one, lol.