Your local service station can supply you with many of the common parts you require; though they stock these parts mainly for their own use in the repair end of the business. The problem, from the consumer's standpoint, is the cost--it will be high. The reason is that the service station operator buys the same part from a jobber that you can buy over the counter. Although he buys at a discount, he must make a profit on the resale of the item, whether through direct sale of the item or as part of repair charges. Really, when your service station sells parts to you over the counter, they are competing with the local parts stores and discount merchandisers, and most service stations do not buy or sell parts in sufficient volume to offer a competitive price. They are in business to sell "service," not to sell parts.