Hi everyone. My SantaFe is throwing a P0272 code (cylinder 4 contribution/balance).

This is the 3.3 V6, so accessing the injectors is a bit of a headache. Car has about 133,000 miles on it. So far I've replaced the coil on cylinder 4, run a 50/50 mix of SeaFoam and Gasoline through a fuel injector cleaning kit, and am currently half way through a tank with RedLine fuel system treatment- the light is still on. I pulled the battery cable to kill the code today, and it came back within about 25 miles.

My questions are:

1) Are there any other troubleshooting steps I could or should take before replacing the injector in #4

2) If replacing the injector, how important would it be to use a Genuine Hyundai injector (at least $350) vs a new aftermarket injector (more like $250) - I've already decided rebuilt injectors are not worth the risk given the hassle of reaching the injectors on this engine.

3) How important would it be to replace all 6 injectors vs just the one bad one on #4 (given the price replacing all 6 makes this a $1500 - $2000 job just for the injectors)?
I know I have to pull both fuel rails, and thus all 6 injectors to service any of them on this vehicle, and I know I need to replace the combustion seals on all injectors.

4) Related to #3, what is the expected lifespan of these GDI injectors?

Thanks in advance for your help.