Are engine cleaning products any good for high mileage diesels?

I have a B8 Audi A4 Avant diesel which has done 80,000 miles. My garage is recommending an engine treatment called Terraclean and I'm aware that there can be big bills on a high mileage diesel. Are these engine cleaning products any good?
Terraclean is to clean the valves and combustion chambers on a direct injected engine, which you have, without taking it apart. But there may be more pressing issues such as a partially clogged EGR and/or a DPF filling up with ash, and Terraclean won't fix them.
Answered by Honest John on

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