Apologies if my reply upset you for some reason. Yes it is a sealed unit but I meant check where the gases flow in from the exhaust and out to the manifold. I would not be surprised to see it quite coked up. I thought you were looking for advice but I'll leave you to it.

Finally though as you're new to diagnostics, I wouldn't fit used parts. Especially EGR valves which are a common fault on these.

All the best.
Matt