If the WD40 gets it working for awhile i would do it again but this time clean it out with contact cleaner after the WD and then find a spray in dry lubricant. The wet lubricant will attract dirt and grime and gum everything back up. If this doesn't fix it for the long term then you do need to replace it.
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1998 EB Expedition 4X4 200,000+, 1999 Windstar 200,000+ (Needs Head Gasket), 2008 Chev Colorado (Company Truck, Really sucks but it's free)
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