Smoking 1984 300D... lots of clues?

[landev]

My '84 300D has recently begun to smoke... 'seems like just as the turbo kicks in. This car has just turned 78K miles, has lots of power and typically idles fine. Lots of clues here, but I can't seem to put them together.

First, it seems to have what I believe is a vacuum leak that becomes audible just before 2.4K rpm. I've settled on this being a vacuum leak as, if I punch on the heater or AC, the high pitched sound goes away until the movement of the mixing door stops... it then returns. Under load, there is no vacuum leak type sound... it's only as load is just letting up that you can hear it. It can't be heard unless the car is moving and at that 2.4K rpm range. I've climbed above and below the car numerous times and applied a smoke machine to the vacuum system and cannot find a leak.

Secondly, there is a slight bit of oil on top of the valve cover near the fill cap. It looks like there is excessive pressure possibly forcing oil out (perhaps this is where my whistling is coming from?) I've also noticed a couple of drops of oil on the floor after running to town and back (~60 miles) then parking the car over night. It's very difficult to tell where the source of the leak is at this point. The oil leak is minor and there is no noticeable drop on the level on the dipstick.

A third clue is that the car runs very well and has lots of power, however, when I get to a stoplight after having run the 30 miles into town, it runs a bit rough at idle... not horribly so, but enough to make the car shake ever so slightly. Upon returning home and, unloading groceries, the car idles fine for about 5 minutes, then starts to idle a bit rough. I did the last valve adjustment ~ 8K miles ago and all seemed fine... the smoking (and other symptoms) just started in the past 300 miles or so.

Air filter looks fine, Diesel Purge didn't seem to help. Again, the car has a lot of power and accelerates and runs well... as long as I don't look in my mirror as I attempt acceleration.

I thought about injector issues, but does that explain the oil issue? I'm completely stumped on this and am toying with replacing the injectors (cheaper than having them tested!) but wanted to field this before throwing parts at it.

Any ideas would be welcomed!

Thanks!

-l-