I finally got to shoot my newly acquired SKS this morning. I purchased it immediately after a snowstorm up here in PA, and was delayed further by some single-digit temperatures and more snow. While waiting for the weather to cooperate, I did some research about the rifle and decided I didn't want the Slam Fire Surprise, so I ordered a spring-loaded pin from Murray's.
Today, the temp hit 55°, so it was off to the Shootin' Hole to check the sights out, and run the 'new' rifle through its paces. Using Tula Ammo, I started getting misfires after about 25 rounds were through the gun, but after re-chambering them, they'd discharge as expected. Coming up on 55 rounds, the gun wouldn't fire at all, which necessitated an impromptu field strip, expecting a broken firing pin. The pin was stuck pretty badly in the bolt, and I couldn't free it up with the rudimentary tools I had in the field, so I headed home for further investigation.
Upon disassembly, the pin came out with a little tugging, but there was no sign of the return spring. using a tiny hook fashioned from MIG welding wire from the hammer end, and some skinny punches from the bolt face end, I managed to extract the contents of the firing pin bore.

I didn't pay much attention to any of the popped primers stories that I'd heard about, but I shoulda. Going back to Murray's site, I read up on the problem, and sure enough, there was a burr raised around the firing pin hole on the face of the bolt. Using a fine jeweler's file and a flat stone, I removed the burr, and then chamfered the hole as seen in the below photo.

I replaced the mooshed spring with the spare that Murray's included (thanks, Ben) and ordered 5 more - just in case. Yeah, I shoulda read more about that primer problem, but, like most people, I figured it wouldn't happen to me.
It looks like the weather is going to take another dive over the next couple of days, so it'll be a while before I run the gun through the wringer again. I certainly hope it's fixed for good this time. It's going to be some time before I can acquire some boxer-primed brass and start reloading my own, thus eliminating this glitch.