Bren

Don't know anyone down your way but when I've had problems like that in the past have mostly gone to Custom Chrome in Nuneaton who keep just about every sort of flange, box and section. They will do either mild or stainless steel. You have to book an appointment but they have always made exactly what I asked for and it has lasted as long as I've had the car at reasonable prices. I think Franklins in Northampton offer a similar service.

Mine did this too, though it's a lot older and I got mine dirt cheap as the seller was honest about it. Also had a slightly lumpy idle in N but not D. I looked through the service history and noticed it had missed the heads re-torque and camchain tensioner replacements. Also noticed that the overflow tank was filling up but not siphoning back to the radiator so my guess was a head gasket issue pressurising the system. Am still waiting for the mechanic I use to have time to fit it in. In the meantime I flushed the cooling system and for 2 weeks ran it with just water and the Subaru recommended coolant additive which turns out to be re-packaged Holts Radweld Plus. I started with half a bottle and added another bottle and a half incrementally as I couldn't see the point in just pushing it all out the overflow tank. No climbing temperature or lumpy idle issues in a thousand miles since including long uphills fully laden with the family on board and a boot full except once in a while it will need a small coolant top up (maybe half a cup) when I also add a small shot of the additive . I normally use a bike so don't rely totally on the car except when it's icy or snowing. If I was in your shoes I'd pop back to the dealer and get them to take it for a run with you to get the problem acknowledged and ask them to get the cylinders pressure tested to eliminate head gasket issues while you're still under the protection of the sales of goods act unless they gave you an excellent warranty. Good luck with getting it sorted. Bren