Pilot Screw seat damage

[robsgreen]

I've finished cleaning my carbs for re-assembly and have noticed on carb 6 that the pilot screw seat looks incomplete. it looks like there was fault in the casting perhaps, but does not look like damage from over tightening? There is not a complete seat for the seal and washer to bed down on. If I drop in the seal and washer , they sit flat and I can bed the pilot screw up to the seat. The height matches all the other screws. Im pretty sure the carbs had not been apart before as every was in very good order but just filthy. The bike had not run for 30 years but had covered 22,000 kilometers. Is it possible this fault was in the carbs from new? has anyone else had this issue. does the pilot screw control flow air or fuel ( forgive my ignorance on this). If its fuel, will there potentially be a leak through the screw? Obviously replacement of the carb is the easy one but what are the chances of buying one carb? i think I run it up first and see what happens.
Any advise, help always appreciated
cheers
Martin