yobbos1,
Just a thought here....try the WD40 again....work the action on all blades 15-20 times....WD40 again... (you should be doing the backstroke in the stuff by now!)....Then blow it out through the backsprings with a compressor, some canned air, or even a hair dryer on high/strong as a last resort.
No guarantee unfortunately, but more than once, I've found slivers of brass lodged between the liners and the backsprings that slow the action until you work them out.
May be worth a try. Good luck.
Bill
P.S.
When you get finished, don't forget to lube the joints with something like Break Free, Militec, or mineral oil if you cut/use it for food.