In reply to message posted by 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.
Thanks for the speedy response, but I’m pretty sure my washers and seats are good – unless you’re talking about the way the bottom part of the removeable seat (shown at the bottom of the first image) fits down into the pipe. Is that what you mean?
P.S. If it was possible for me to call a plumber, we wouldn’t be having this conversation.