I soaked the fittings on my oil cooler lines (both at the cooler and the oil filter housing) daily for a week with Kroil before my indy replaced the lines earlier this summer. I don't know if the shop did anything other than wrench the nuts loose, but I got lucky and they came off without any problem.

Good luck with yours.

Charlie

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05 E320 CDI - 185K miles
82 300D - 200K miles (sold)