You have asked me a question I can't answer, but I would offer this: When trying to troubleshoot something, don't mix things up. If you settle on one type of line use it throughout.

What you are trying to do is pinpoint a problem. By making additional changes you might be compounding a problem. Use a methodical replacement method and stick to your decision. That way you eliminate things one item at a time.
Better yet, ask for a knowledgeable opinion here on the "board". Good heads prevail here. Good mechanics with vast experience. Technical questions are best lleft to them. I am a shade tree mechanic. Not a very good one at that. An auto mechanic is the same as a Doctor. They are skilled, knowledgeable and have EXPERIENCE! It's what they do so it stands to reason they know more than I do.

The thing to remember is that a 560SL and moreso for a 450SL is that they are OLD. Old means things wear. Even if a car sits from new, items deteriorate especially rubber hoses and tubing. Pay close attention to things that wear. bushings, washers, any thing that moves frequently. Regardless of the material, with few exceptions, things age. I do, you do, and so do 560 and 450 SL's

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1988 560SL
Black Pearl/Palamino