My 87 420 SEL with 200K has been running fine, no problems and no oil consumption. The other day it dumped, literally, several quarts of oil out of the dipstick hole...obviously there is some pressure build up in the crankcase...I don't think it is blow by because this was so sudden and so dramatic...I can't see anything wrong except the air pump is not working but that has been the case for some time. According to the Mitchell's book, the crankcase vent system looks pretty simple but Mitchell's doesn't explain the connection between the hose from the valve cover and the mechanical cylinder that it hooks into...my guess is that what is happening is that there is an electrical problem that is closing off the mechanical cylinder and not letting the crankcase vent properly. It only does it when under power, not when idling. Its a mess, though, and I can't drive for more than a couple of miles without all the oil shooting out of the dipstick hole...that doesn't sound like blow by to me.
Thanks in advance for any suggestions.