That's a good looking handle there! Sorry to hear about the sluggish closing. I've had more than one knife do that. It is possible that there is a small piece of metal in there causing that. I've had a few knives where they had to be flushed and worked for quite a while and then suddenly they worked just fine. If all else fails, you could try wiping some flitz at the sides of the tang and then cycle it open and closed. It would need a good flush after that kind of procedure.
There are many threads here about this very topic. Everyone seems to have their own method.
Here is one such thread:
https://www.bladeforums.com/threads/flush-or-dont-flush-gec.1081109/
One fellow suggests boiling your knife. DO NOT BOIL YOUR KNIFE!
Chris, who was a longtime GEC employee, always recommended using WD-40. My own personal method is to use plain mineral oil. Get a toothbrush, dunk in the oil and brush into the joint. Cycle, wipe, repeat as necessary. I've sold a lot of knives over the years and I've had a lot of people comment about how well preserved they are. That's from wiping the blades and springs with mineral oil and leaving them that way while in storage.
Mineral oil is available at any drugstore in the laxative section (yuck!), it's cheap, food safe, does not become gunky or sticky over time (like 3in1) and never goes rancid like olive oil. It's a little messy but wipes off easily enough.
Toothpicks, gun cleaning patches and pipe cleaners can also help. Beware of using rubbing alcohol on acrylic. Hope that helps.
Knife content:
My absolute favorite Northwoods knife ever, and one of my favorite GEC knives of all time is this Esky Zulu. Wouldn't mind another run of them someday.