If the grips are wood, rubber (or anything worth keeping for that matter) remove them. Spray it down with a product that will
penetrate the "gum". Anything from Ballistol to PB Blaster will work... just something that will soften/dissolve the varnish/powder/grease/gorp that causing the bind. Hell... even good old WD-40 will work in this context.
Cheers,
C