To troubleshoot my electrical problem on my 1959 220SE I need to remove the instrument cluster to test my ignition switch, and to remove the cluster I have to remove the capillary tube from the engine but when I try to loosen the attaching nut the tube moves with it causing the tube to turn with the nut which will break the tubing releasing the gas from the tube. Any ideas?

I was able to remove it although it will no longer work. Not much action on this forum I notice.

not that many peeps with a 1959 MB online..

Good luck I would have soaked it with PB blaster and other miracle spray lubes/penetrants etc.
wiggle nut back and forth.
Light taps on nut sideways
Maybe scrub a little bit with brass brush.

And repeat them often to loosen the rusts hold over the tube end.