The 730d can suffer turbo failure ,Also inlet manifold swirl actuators can break off and be ingested by the engine necessitating a new engine at enormous cost.
Im afraid your problem isnt unheard of, a lot of BMW diesels suffer the same fate, and BMW know about it, but no recall was ever issued, you could seek legal advice as I suppose your case could be it should have been checked at every service but the problem being there's no proof it was or wasnt..I think your looking a new engine or 2nd hand one to be honest as my experience of BMW they dont do rebuilds they just replace...so maybe you could get the engine rebuilt elsewhere it would cost a lot less than a new one for sure.
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