It is not unheard of for XTs to leak high voltage at coil/HT lead, particularly the connection between the two. When it's dark, can you see any tracing (blue cotton'like threads of electrical charge) on the coil body or HT lead?

I wouldn't put oil on it though. Give it a spray of WD40 or similar to displace any moisture. Better still, dry it all out and coat the joints with silicone grease to seal it against future water ingress (if that's what the problem is).

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