Hello all, just bought a 79 450SL..Oil pressure is fine when car is cold and on high idle but once it warms up and the idle slows down the oil pressure drops to below 15psi accompanied by engine ticking..I am gonna change the oil first to a thicker oil because when I take out the dipstick the oil drips off like its water..gonna try some 20W-50..incase that dont work, how hard is the oil pump to change on this motor 4.5 liter? Thanks for any help or advice..