Hi,
You need to strip down that gripper bow assembly completely and wash it in warm soapy water to remove any trace of lubrication when the components are dry check the parts for any wear especially the cam & tunnion gears. Replace any worn parts and rebuild the assemby, put a small amount of high melting point gease in each end of the trunnion casting (this is the only lubrication require on this assembly) I suggust that you remove any of the silicone spay off of the mechanism, it may have worked but it is only a stopgap solution and not a fix.
Regards
Alan
Alan Hood
ami-man
UK