PhilB, I've got Halford's semi synthtic 20/50 in my Dodge WC51. That is good stuff and keeps higher pressure after a long run than my previous Valvoline straight mineral 20/50. My new WC54, is running on Straight 30 , pressure from certain respected members here, . So far she hasn't had a long run on fresh oil so I can't compare, but a recent 88 mile run home from Portsmouth, on oil God alone knows how old. Pressure stayed a steady 55 lbs all the way through. I have now flushed the engine out and changed oil and filter There was nothing nasty in the mix, apart from the colour. The one thing I would say is a motto painted on the wall of the enginnering shop at college, 'Good oil and greas are cheaper than repairs'.