I have a 92 190E2.6 that has had very mild stumble/rough idle. Other than that, the car runs very strong. Plugs are new and this started at 60k and the car now has 75k miles. I scoped the secondary and cylinder #1 had an erratic waveform. Pulled injector #1 out and placed in a cup with engine at idle. the injector spray was just a single stream and went to an offsided spray once rpms above 2000. What is the average life for mechanical injectors? These are the brass injectors with the tips being steel. Should all the injectors be changed at the same time to keep uniformity in all cylinders. Thanks.