I recently purchased a 1992 400E w/ 63K. I will be changing the oil and filter this weekend and would like to change to Mobil 1. Is there a problem w/ this change? Further, assuming I switch, how often should I change the oil and filter? Finally, does the old oil have to be drained via a Topsider device from the dipstick tube, or, can you just remove the drain plug from the oil pan and let it drain the old fashioned way? Thanks you any help.