Emission Systems For Cars And Trucks Cheapest Parts On the Web

I have 8 valve turbo GM diesel astra which has problem with Exhaust Gas Re-circulation valve. The engine management light comes on a lot (ie the valve isn't closed) MPG isn't good and when light is lit acceleration it VERY poor! I KNOW the egr valve is to fault BUT on this model the egr valve is part of the inlet manifold! It can NOT be changed & an inlet manifold is £580.00. If I get another inlet manifold it could go again, and again! I could cut the valve off and get another valve fitted after welding a flange onto the manifold but what valve would I use? Is there any way around this? I could remove the manifold and soak it in something to clean it but when it happens again, then what? I've tried sealing the actuateing pipe but it doesn't work. I drove nearly 200 miles this weekend and the light was on almost ALL the time! I've played with cars for 25 years but this is driving me nuts! HELP!!!! Car has only done 70,000 my last astra did 220,000 and still returned 55MPG