420SEL burning oil

[mdawson]

I have a 1987 420SEL with 235k miles that I have driven daily since 2005. It has provided safe and reliable transportation for these last 12 years but it has suddenly started burning oil, but only under a very specific set of driving conditions. Most of the time it doesn't burn any oil or make blue/white smoke, but if I get stopped in traffic and am pointed downhill for more than a minute or two it loads up with oil into the cylinders and when I hit the accelerator and drive off it produces an unbelievable white smoke screen that lasts for more than 30 seconds and starts to clear up slowly turning from white to blue then clear. It will also load up the cylinders with oil if I coast down a steep hill and pull the tranny down to 3rd or 2nd for compression braking, when I press the accelerator down at the bottom of the hill it blows a big cloud of smoke.

I think it's most likely the valve guides are worn and it's pulling oil into the cylinder that way. Do you guys have any ideas for what else it could be? I've religiously serviced this car changing oil every 3k miles with Chevron oil. This might be the end of the road for this old boy as it's not worth the cost of having the heads rebuilt.