This is in the 240D.

I have never done a compression check, but it will start right up even in cold (say >50* for here ) weather without glowing at all.

It has always used a good bit of oil, like a quart every 500-700 miles, and I used to be able to see a puff at high RPM right before I shifted gears (MT).

I just followed my wife home while she was driving it and there was a pretty steady stream of oil smoke coming from the tailpipe. I know it is oil b/c of the the smell.

What are the likely culprits? How do I start diagnosing?

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT