I just started the engine after replacing the oil cooler lines on the SD. The lower (tructec brand made in Germany) is leaking at oil cooler the fitting. Apparently the surfaces aren't mating as they are supposed to.

I disconnected the leaking fitting, checked both surfaces for contamination and reinstalled. I tightened as much as I was comfortable but didn't want to strip the cooler. I also turned the line as I tightened the nut hoping that it would seat better. (works on Cummins fuel injection line) It is still leaking.

Anyone have any sealant or methodology that would be acceptable?

This is a compression fitting and is normally installed dry with no sealant.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.