Rear axle lockup

[402Bowtie]

Hey guys and gals - can you help me?

What happened:

I coasted to almost a stop (5 mph?) in my 72 C20. Right before putting the clutch in to put the trans in neutral, the truck lurched to a complete stop while making a grinding noise coming from the rear of the truck.

I was able to put it in neutral without issue. I then easily put it in gear to try driving slowly, but the truck did not move, and you could feel it was "stuck." I put it back in neutral.

I got out of the truck and tried to push it while in neutral -- still felt stuck regardless of which way you pushed the truck. Checked the driveshaft and all looked good.

A few other guys helped me push it, at which point, it eventually broke free and rolled smoothly.

I put it in gear and drove 15 minutes more to get home. After starting home I could hear a rotational, metal-on-metal, scratching noise which eventually went away after the first few minutes.

Today, I finally opened up the rear cover expecting to see loose metal pieces, but everything looked good to my untrained eye. I jacked up the driver rear wheel and spun it by hand and watched the gears rotate fine for several revolutions. Did the same thing on the passenger side. No metal, debris, etc was found.

What do I do now? Fill it with new lube and drive it? Where else could it have bound up?

I believe it is a HO-52 rear end with coil springs.