(Found) Valve seats for Impact

I just installed a new valve seat in my Impact and it's like having a new gun. It's been really hard to find someone who is making an improved version. Steve at Pomona airgun is making them now. So if your looking....
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How much are they and are they in stock or special order? Was that all you had to change or were their other parts to get it to shoot like new again. Also a stupid question but how many rounds before you had to repair. I have heard that this a common problem with the impact. I just bought one and have had some problems with mine and may need to do some preventive repairs with some better parts. Any info would be very helpful. Thanks for the imput.
 
OK guys here it is....the valve seats are made of brass with a broader shoulder which makes them a little bit longer with a slightly larger inner diameter for more air flow I'm getting 945fps with .25 kings 25.4g.. My original valve seat broke early on after about 6 tins of pellets. And he also replaced my hammer bumper O ring with a high strength nylon because it was flat.