LindaJane,
Typical leaks for the 617 5 cylinder engine are:
1. Front Crankcase seal - Not too expensive to replace.
2. Turbo Drain line seal - cheap parts but can be labor intensive to replace.
3. Oil Filter case seal to the block - Again cheap part but a pain to replace.
4. Oil cooler line fittings both at the oil Filter and oil cooler. - A little expensive to replace.

As suggested before, clean the engine and then determine where it is coming from (or have your mechanic look after your cleaning). Also - Switching to a synthetic engine oil such as Mobil 1 has been known to eventually seal some leaks. Hope this helps.

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D. Blake
86 300SDL 340K (for sale)
83 300SD 205K (gone)
06 Chevy K3500 LBZ CCLB 50K
94 Chevy K2500 6.5L TD 250K (gone)