Hi Jules-----Got yourself a Webley pistol then? .The sears all go like that. When you think about it the curve of the piston has to sit in the curve. I not sure whether that sear is sintered or not, but generally, any grinding or filing of a sear is only a temporary fix.
I'm not sure about the seal---I'm sure I have seen blueish ones though.
Is the Premier a Mk1 (all Steel) or a Mk 2 (Steel and alloy)? The all steel ones are ok, but I am not a fan of the Mk2 2 as I've seen a couple with the sear pin in slightly the wrong place so the thing won't cock of function properly. Also, BlOODY SERRATED trigger pins going into alloy
Even if you use a dry moly on the piston/ cylinder, Webleys always seem better with some thickish oil in them . I think the factory used straight 40 engine oil. I use chainsaw oil as I have some here.