For Several Months Have Experienced A Bad Tasting "leaking" Into

For several months have experienced a bad tasting "leaking" into mouth from under a crown located lower left side(not wisdom tooth) . Leaking Comes from same spot 24/7. Dentist has replaced crown three times, took full mouth xrays says teeth are alive and good. No need for root canal work. Perplexed. On same medications for years for high blood pressure and cholesterol. Fear internal health issue such as cancer. Help.