Start problems with Peugeot 407 SW

Hello, who can help me? I have a Peugeot 407 SW Diesel, B.J 2006 because it first sprang after many start attempts. my lion has 116500 km, this week was the one at free workshop 2 days was looking for the error and found nothing which have separated complete diesel line up to the injector and connected a tank with diesel then everything has worked freely as the told me. After that a seal on the line was replaced and it worked r for 2 days after that came the same problem again. Again with the workshop on the phone and I was told that I should replace completely from the hand pump to the injection with housing for diesel filters. Just I tried to separate the line from fuelilter and plug it in together without the fuelilter, it did not bring anything the problem is still there. My guess is now that something has to do with the starter, because if I want to start the engine The battery was tested yesterday and that’s Ok which was changed a year ago. Thanks in advance for your answer. I’m sure you’ll be happy to hear from me.