racefanone
If you are using a flat washer ,try a beveled one,or vise versa.Make sure the seat is not chipedor gouged in any way.If seats are removal,replace them,if not you might have to dress them with a seat grinder. Change both hot and cold sides.The leak at the packing nut can be fixed with string packing or a new packing gland.Might be best to call a plumber ,you could make things worse and then it could cost you more in the long run.Just my two cents worth. 
