Having trouble with a dripping cold tap on kitchen mixer type, got valve out put new washer on as old one scored. Looked at valve seat and it looked rough in a couple of places, got a reseating tool from Screwfix and had a go at grinding it. It cleaned some parts of the seat but not the rough looking areas. Gave it another few turns but still looked the same. Put valve back in anyway and turned water on, still a drip but also now have to turn handle numerous times to turn off and on unlike before. Worried now that I have taken too much off the seat with the grinder despite the rough area still visible. Not sure what to do next. Tap is 26 yrs old, replacing it could be tricky for a plumber as there is alot of pipework under the sink. Have looked for a tap before but it has to be white to match the sink, also cannot find one with the spout length that the current one has. Tap is a Paini one, even their equivalent one now has a shorter spout and is over£100 anyway. Any advice welcome.