This is the cars second engine.Last owner had it changed at 190,000 miles.This is another 68' engine also,mileage unknown.Car has 220,000 now.Last owner used whatever brand 30W was cheap at the gas stations.Yes I'm using Rotella 15W40.Mobile 1 in all my non diesels.Gapless rings are top compression rings,but would help with oil controll also.Good to know someone else has tried them with good results,thanks.And I'd never heard about weak,poor metal engine castings before.Good to know.I'm used to big industrial diesels.Semi trucks and my 71' Kaiser Jeep Mm35A2 Military 6X6 multifuel truck.Any Mercedes Diesel info is welcome.Worked on MB busses,trucks and semi's.But new to their cars.