I am using the Quaker State DEFY 5W30 in my '80 Firebird FORMULA V8/4-bbl since I did this OCI in July 2012. I haven't driven the car since late OCT '12.
No changes in my oil dripping from the MaxLife that I was using prior to the DEFY but, time will tell(I'll see next Spring/Summmer/Fall).
3 prior OCI's/Summers were with MaxLife 5W30 which had slowed down my leaks but, didn't stop them completly. The ML also contributed to making this engine quieter/smoother from the other conventional oil I had been using...all name brand oils held in high regard here at Bob's! But, mostly Pennzoil Conventional and Havoline
What I have noticed with the DEFY is, how much quieter/smoother the engine is, even compared to the ML. This particular V8 engine(4.9L/301cid) has never been this smooth in 32 years.
I am noticing this quiet & smooth with most Quaker State oils in general(Quaker State Ultimate Durability, Quaker State Conventional) in my other vehicles lately. I have used Quaker State oils in the past in many vehicles but, never noticed as much, just how quiet my engines are these days while using Quaker State oils.
I have also noticed that some oils make the engine more audiable compared to the oil that I just drained out. Quaker State oils seem as quiet as the better or quieter oils...I can't explain this exactly
With most OCI's, the engine(s) seem the same in terms of smooth/quiet. Amongst a few other brands/wgts, Quaker State oils are the quieter oils I've used.
I have a keen ear and pay close attention to noises in my vehicles. Noises meaning: NVH, squeeks/rattles etc.