i know this one person who bought an 87 528 e with about 225,xxx miles. i'm pretty sure it is full of sludge,gunk,etc. they do not change the oil when needed,just add when it's low.it is driven now mainly on the highway,about 30 miles each way.what is the best oil to use,so that all the crap inside the engine will start to dissolve,and run better? i guess i will have to change the filter for them,since they hardly ever do it. i do not think they would want to buy auto-rx,since they are not into engine oils.