I know it sounds harsh but i agree with Ekona, if the deposit was fully refundable in these circumstances then there is no point in it in the first place. It's purpose is to safeguard the seller and give the purchaser security on the purchase
I would discuss the matter with the garage and state you are willing to pay for the work done and reimburse time and effort on their part and hope they accept the offer and as a goodwill jesture of goodwill give you some of it back.