I'll leave the injector questions to the techs. However, you may find some valuable insight into that issue by searching the Shop Forum records. (search function in top right corner of screen)
Best brand of gas is a "politics and religion" debate for the most part. Many Porsche buffs seem to like Amoco and Chevron. I don't seem to notice any difference as long as I buy a name brand (Amoco, Texaco, Exxon, Chevron, etc) and premium (92 or better octane) grade. I remember my ex's old Honda would have more engine trouble when it ran on XXX brand gas vs mid-grade Exxon but I think that was due to the higher octane rating rather than any specific brand quality. Based on what I've heard and read, most of the gas you buy is the same wherever you go. It is just that certain brand names have different "additive packages" added (duh) to them. Those additives are what differentiate one brand of gas from another.
Hope this helps...Lee
P.S. Be sure to search the shop forum for references to your injector question.