I had exactly the same problem. Although that gear was worn-down a bit, i discovered it in time and could limit the damage.
This was only after 6 months of use or so! I contacted petsafe and overstock.com but they wouldn't send me a replacement part, nor offer any warranty. After i cleaned that gear it still seemed to operate, so i decided not to take further action...
Now, after 1.5 years, the other gearbox started grinding and broke down after a week or so. (this is the gearbox of the transporter)
The warranty is 3 years, so i contacted Overstock.com again... Overstock send me to petsafe... petsafe told me I had no warranty since I was an international customer and it was 'illegal' to ship it to other countries because of FCC regulations.
But because i'm from the netherlands, my only option was to buy the unit from overstock.com. The unit normally is 100 dollar or less. However, in euros its suddenly 90 euros ( 118 dollar). Also the shipping/handling was 58 euros. (65 dollars) So i paid 194 dollars for something that normally is 100.
After their no-warranty reaction, I replied with a lenghty mail, asking critical questions about WHY overstock was allowed to sell me the (now "illegal") unit in the first place, and WHY they never told me I didnt have warranty.
After that, without repsonding to my questions, they told me to ship the unit to engeland (another 26 euro/34 dollar), and they they would pay me back the 90 euro. (118 dollar)
So instead of sending me a replacement, they 'limited' my damage to 84 euro (110 dollar) instead of the full 194 dollars.
Safe to say i'm NOT happy with this situation. The product just has a bad build quality. Dont get me wrong: it works perfectly (if you use the right kind of litter), but the gears are just cheap plastic shit that break down too easy. I cant imagine any of these devices can run for 3 years 24/7!
I wouldn't mind if they just made the warranty one year and offer me a way to buy new parts for a normal price, but thats probably too much hassle for a big company that just wants to sell units. They should just allow a reseller to sell parts on ebay or something..