I took it to a mercedes independent shop, they insisted on checking the compression before working other issues. With the injectors removed, I could see all 5 injector glowin orange. I saw the links between the 3-4th injectors getting too glowing hot. (I wondered if there could be a partial ground between the loop and a carbon buildup, but I am a DIY guessing)

There is a washer like gasket at the botttom of each injector. I read that it should always be replaced. Instead it was reused, could reusing that gasket drop the compression enough to matter?