Sounds like the seals(rings) on your turbo have gone bad. That is one reason you see oil at the end of the exhaust. Another reason could be excessive blow-by which would be caused by worn rings, which would cause low compression and make the car hard to start. You say it starts easily at 25F,so the comp. must be fairly good. You can do a comp. check(24-30bar).
If you do need to rebuild your turbo, don't despair. There's not to much to it. I rebuilt the one on my 1982 300D turbo last summer. Cost of parts:$22.63. And that included shipping. If you do rebuild your turbo, just be sure and mark the parts before you take it apart. If you want the address of the place I got the parts for the turbo, let me know and I'll send you their toll-free phone number.
Bill Lewallen Lexington,Ky. Where diesels purr and turbos whirr.