Mini R56 (2007er) does not pull, control chain defective???

Moin, my friend’s mini can’t drive any more. The following situation: It was only a slow driving … not faster than 20 KM/h … possible. When starting the engine raced briefly and he didn’t pull properly. At one traffic light the engine went out and could be started again after a little time. After that my friend could only drive home at very low speed. The engine could only be driven underboard. It did not light up any control lamp during this whole time. The mini was towed to a workshop. Result: too little oil and the control chain should be renewed. Cost 1.90€. The magnetic valve was already changed for 160€ and did not bring any improvement. What do you think of the workshop diagnosis? To the Mini R56: 120,000 KM, N12, 1 year in possession and very well maintained. Can it only be located at the very low oil level that it is no longer really mobile? Or can it actually be located at the control chain? That had not caused any problems until now and was not heard before. Anyway, I want to change it from the ‘favorable’ workshop and then.