Once had a reoccuring problem with the spoilers on the left wing sitting slightly raised...would stow with slight control yoke movement. This was evident during the preflight.
Engineering was told and noted in the tech log.
6 to 12 months of continual reporting/investigation with no result...."report further"
Finally someone in engineering made the discovery.... a FROZEN RAT lodged in and around the spoiler controls.
Persistence pays off...