Got my mom's 2003 buick park ave 3.8 base. It has 98k and always dealer serviced with acdelco 5w30 syn-blend. It has no leaks, no smoke.Would it be ok to switch "cold turkey" to M1 10-30 syn HM or does it have too many miles?Or would it work out better to gradually switch to Full-Syn-HM like first change the oil with 3.5 qts of 10-30 Syn-Blend & 1 qt M1 10-30 Syn HM? The oil capacity is 4.5 qts. This is such a good/nice car, I simply don't want to start any crap with this gd engine but on the other hand I would love to get 300k mi with this nice full-size car.Â