About 2 or 3 tablespoons worth eery 500 miles. I know this is caused by something simple but I don't know what it is.

its the oil vapour from the pcv valve that is condensing and gathering as oil. Your pcv vlave may be blocked, or you have excessive blowby. If it is blowby it will be a rebuild job.

Blow by is caused by compression leaking down past the piston rings into the crank case, and up past the pcv valve and into your air cleaner box.

HTH,
Chris

I have oil in there too. 1984 300D Turbo. I noticed the tube going towards the turbo was melted, at the tip. I cut off about an inch and put it back in. What's that caused by.