hi, couple of weeks ago my bmw 320d started having starting issues as in it would take a good few turns when cold before it would start. Its great when its hot or warmed for a few mins. So i changed the set of glow plugs with wellman brand ones, this worked and the car started fine.the dde light would stay on a few secs on ignition and it would start easy. Now after just a few weeks the dde light flashes momenteraly and then it takes a few turns to start. Can you test the glow plugs without taking them out? Btw all 4 original glow plugs were not working when i took them out as i tested them on a battery.