The seal deterioates and the leaks start..MAYBE changing the fluid will help them last longer. I was tempted to put some of that stuff that swells the rubber seals in mine but never did. Drove it 6 months with a slight leak, then it got bigger...so I replaced it. If its running fine dont bother with the injector flush. I did mine because I forgot about changing the fuel filter until 90,000 miles and was towing a small boat I could really feel the stumble so I had them cleaned with the toyota flush stuff directly into the fuel rail, that fixed it..several bottles of Techron did nothing at all.