I had a similar case when the lights in the cover of my aquarium stopped working. It looked like a faulty starter motor, but in a master-class of product design, the cover was moulded plastic and you couldn't get in and change it.

I took it back, but had no proof that i'd bought it there. They only recognised me as a semi-regular face in the shop.

After a little umming and ahhing, they gave me a brand new cover, completely free of charge. I was very pleasantly suprised.