To my knowledge the best is ''Expert Stylus&Cartridge Co.''
They first inspect the cart and then give you the best advice
they can. Besides they do the ''real retip'' with their Paratrace
stylus. That is to say only the stylus in the existing cantilever.
The most other do the more easy job by gluing the whole new
cantiever/stylus combo instead. Curiously this is more expensive.