I'm driving a 1992 Volvo 240GL with 215K miles on it and am considering switching to a high mileage oil. I'm gonna guess that I burn through a quart between 500 and 1000 miles. When I used the "Find the right oil" link on the Mobil website, it selected Mobil Super Synthetic Euro 5W-40 (only viscosity offered) although it doesn't seem to be available when I search online. I've never used synthetic oil in my car and read that it could possibly cause leaks instead of fixing them. Is it safer to go with a non-synthetic high mileage oil? And viscosity? I live in New York City so we don't get super cold here (might drop to single digits on a couple of winter nights) on rare occasions) or hellishly hot (rarely breaks 100 degrees). Any suggestions would be welcome. Bill