Blown Head Gasket problems of the 1999 Suzuki Esteem

The 1999 Suzuki Esteem I purchased started havin g trou ble keeping up speed on 5-29-02,they refused to even look at it, until a month later when I went back up there again. The problem with the car is htat there is sealant on the #1 plug, and all they say is wrong with it is the #1 fuel injector,which they want $500. 00 to put it in. Ive had at least 3 other mechanics tell me that the head gasket is blown, or the head is cracked on the car, and the dealership I bought it from refused to check it out.