[Drisump]

Petr, I don't know where to go from here, the mystery of the disappearing oil is large enough all by itself. Have you checked your coolant...I suppose it may be possible that you have leaked the oil into the coolant system. And this would likely be caused by a blown head gasket. I didn't ask this before , but is this engine turbo-charged? The oil light staying on means that either the engine is not achieving the minimum oil pressure to run, or the sensor or the wire to the sensor is damaged. It's possible that your engine has a low pressure cut out, which may explain why it won't continue running. Diesels operate at a very high compression ratio (probably 20:1 or so)so bump starting them or turning them over by hand can be a bit of a chore. You may want to look in the general areas that the mechanic was working in, perhaps a wire has been knocked loose. This would not explain your starting problems but possibly your continuous running problem. The starter can be still at fault despite working fine once or twice, starters at the end of their lives, develop dead spots on their armatures... sometimes striking the starter with a hammer while trying to turn it over will get them going. I would check my battery connections and all grounds....by checking, I mean disconnecting them,cleaning them well before reconnecting. If the engine was bound up .....it is toast, but given your description of how it sounds when it runs, I don't think so. Good luck and Happy New year