I am completing a top end rebuild on a high mileage ZX6. When I got the bike it would not start from poor compression because only a couple valves were still seating properly through all the carbon build up. Question I have is can I use these old exhaust valves with heat damage over again? I replaced one because it actually had a hole through the face but the other just have slight face warpage, but still seem to seat flush against the head. I would replace them all if I could but at $37 a piece that would just be stupid.