Hello--Iv owned a number of volvos over the years and have used reg oil and changed at 3000 miles with no problems. I still use the reg oil in my 160k mi 1980 244GL,but, have switched my 945 turbo (99,000 mi) to mobil one a few oil changes ago after reading that it is beneficial to higher mileage cars as well. Just curious--would most agree with that changing to synthetic as I have will prolong turbo life. Since switching to mobil one-havent developed any leaks and overall --I would say that the eng actually runs a bit quieter now as before the switch--I sometimes had a little tapping sound just after start-up. Just curious as to whether or not I have done the right thing. I guess I should have asked this question before switching to mobil one--guess i got caught up in the advertised benefits--thanks for your opinions.