Whenever you hit the fuel system with the "strong solvents" you should always change the fuel filter. I hit mine twice a year with Techron and change filter right after that tankful. I use STP gas treatment about once a month through winter & maybe twice during spring->fall. It just keeps the system clean and you can never trust the quality of the stuff coming from the pumps. I guy I met in Orlando has an '89 E34 with 360k on his ride & it has original injectors and they're like new using the above routine.