Dumb question, BUT ... my 1960 MGA oil pressure has dropped since I changed oil. What's up with that? When you first crank it up, pressure is about 70 PSI ... as you drive and it warms up, it slowly drops to about 40 PSI, and stays there. No rattles, no smoke. I think it showed higher PSI before the oil change....I dumped in 10W40 detergent, Valvoline. Thanks, MG