[Vwdiesel] SL and CD Oil

[Rudy]

A while ago there was a discussion about using SL (spark ignition) and CD
(compression ignition) Lube Oil in VW Diesels.  
 
My 84 Jetta TD is burning a lot of Oil now and I'm waiting for a window to
rebuild it.  I've been using Mobil 1 15-50 which I need for the low Oil
Pressure, 15-40 is too light and am concerned about the Turbo.
 
The only other 20-50 weight Oil available is API SL.  Could someone refresh
me on that discussion please?  I don't know how to search archives or even
know if they exist.  Sorry to rehash this thread but some input would be
helpful.
 
Rudy