Apologies, I assumed your car was an automatic for some reason.They were fitted front and back by the Toyota dealership. I questioned them when they said they were fitting fronts as well because I know from this forum that everyone has only received rear sensors but they simply said that they had been authorised to fit them front and back. The rear sensors look the same.
It's good you managed to get both the rear and the front parking sensors installed for free.
I think the only way they'll be able to fix them now is by having fresh ones painted again, as parking sensors are very particular about the amount of paint coating that's acceptable before they stop working properly.
