I suspect its loss of compression get mechanic to check even if he has done past visits and found nothing. Read up this site to see how it works and look for compression faults.
I had in my time 20 old bangers road worthy but needed nursing. One 1949 standard flying 12 nice runner. Other two had faulty valves cleaned them re-seated them fine started straight away) sometime they woul run on 3 cylinders. However I think diesels need all cylinders.
Take a look on this site give full cycle of working of a diesel engine. www.kent4x4offroading.co.uk/how_does_a_diesel_engine_work.htm if it doesn't come up in your search engine box type how does a diesel engine work then look for the above website.
sorry doesn't show faults but may give ideas what to look for try another mobile mechanic or get hime back show him the info on the site.
bob
August 2012
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