Also check to see if the bolt release tab is binding in the bolt stop groove. Slightly bending the tab can do wonders if it's binding.
Sitka is right about stuff like WD-40 gunking up the works, causing the bolt stop to stick. You about gotta take it apart and sometimes it takes steel wool, etc. to get that varnish off the parts. Blasting it with brake cleaner, etc. usually doesn't cut that stuff.
Use WD-40 on farm equipment, keep it away from padlocks, guns, anything with small parts that interact.
DF
