I've seen a lot of posts about diesels and oil pressure, but not much on gas engines. My 73 450sl used to idle at about 30, and otherwise run at the max 45. Now, after switching from regular 20-50 to 5-30 synthetic, it idles at about 25, but still goes to 45 otherwise. The engine has about 112,000 miles. Is the drop in idle pressure anything to be concerned about?