Do you think it really matters much if you use a different brand of top off oil other then what is in the sump? Let's say you are 4,000 miles into a 7,500 OCI and running QSUD 5w30 and add 1 quart of Motorcraft simi synthetic 5w30 Are you messing up the chemistry of the QSUD or after 4,000 miles does the chemistry of the QSUD even matter all that much?