Effects of "high mileage" oils...

Jun 22, 2008
Central Valley, CA
Anyone know how long the effects of "high mileage" oils tend to last? For example, if a "high mileage" oil decresed oil loss by 75%, will that effect continue after switching to another oil in a similar viscosity? Or will I have to continue HM oil use to keep the seals "conditioned"? Specific car is a 240k+ '97 MB with inline-6...always run on Mobil 1. After switching from 15w50 to 10w40 HM, oil drips decreased from 2-3 drops per night to 1 drop every few nights. Would switching back to 15w50 increase oil seepage to what it was before, or would it likely remain as it is on the HM oil?