The original formulation of WD-40 was notorious for turning into varnish muck like the varnish from leaded gas formed on your car's carburetor. In the late 70's early 80's I was working in the gunsmithing shop at Browning Arms in St. Louis, can't tell you how many BT-99 trap guns I worked on whose actions had been rendered inoperable from accumulations of varnish from WD-40 use. I'm told that sometime after that period the formulation of WD-40 was changed so that varnish formation is no longer an issue.
