I have a nasty feeling that you may be right (as I have already explained to the customer-who is an electronics engineer, so actually understood what I was talking about!)

I still live in hope that sorting the exhaust leak will fix the problem, but I am not holding my breath!

The cats were (aledgedly) changed because the exhaust was in rotten corroded condition and replacing the back box ended up requiring everything else being replaced too! (yes, erm...)

I never saw the exhaust before it was changed so I really dont know...

PS I just have the horrible feeling that this is going to end up as one of those "Piggy in the Middle" situations where it is going to end up as being "My" responsibility to negotiate between pissed off customer and reluctant KW, and if it doesnt put the light out it will be "my" fault! and even if everything works out fine I will never be able to charge enough to cover the amount of hassle! (a bit lke dealing with those dreadfull "mechanical break down insurance" companies!)

(Actually, I think the customer realises "exactly" how dificult this sort of fault is to deal with, so it might not be quite that bad! )

Sorry its late and I am a bit, You know!