My 1999 Accord with V6 and 240,000 miles pings on all gas except premium.
I removed the upper intake manifold and found a very small pool of oil in the mainifold floor next to the opening that the throttle body bolts to.
Also there is a small port in the upper manifold next to the throttle body opening that is about 80% clogged with a hard black deposit. This deposit is also in the corresponding port on the lower intake manifold.
I had a new EGR valve and decarbonization done at about 175,000 miles.
The car runs great on premium gas but it is supposed to run on regular which is a lot cheaper.