It sounds like the endpin rod may be bent slightly. If the rod is removable, roll it across a flat surface. That will point out where the problem is located if it is bent. Straightening a bent rod is not all that easy and straightening it may not be possible. A visit to your local luthier is probably the best action. WD-40 is not the answer.
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95% Retired Midwestern Luthier
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