What oil do Honda dealers use?
Most likely, the cheapest API certified oil from whomever wins the contract bid.
Why would they do otherwise when, with one exception, Honda engines have no special oil requirements?
Perhaps an Acura dealer would have some special oil in stock for the RDX.
The Honda dealer here used Valvoline last time I noticed. I never used their services for an OC.
Ashland (Valvoline) has some headquarters in town here too. Probably some product research facilities.