I would be worried about the splines as well. If you're on the trails and you lock the rear, it will probably engage fine but it may have a hard time trying to move the collar back when trying to disengage. Especially if you stress it, twisting the splines more when it's locked.
I'm sure it's fine for a while just driving easy on it around town if needed.
I have no experience with this or 80 series to be honest. But I do know that It takes a lot of stress to break an axle. They aren't designed to twist, neither are the splines. Some time in the past your axle was stressed 'almost' to its max and didn't end up breaking. It will be a lot easier to break since its already tweaked.
Thanks, guys. I reinstalled it for now. I was worried about being able to get it back in, but a few minutes of fiddling did the job.
The rear locker has worked pretty much flawlessly since I've had it (about a year) -- sounds like I'm kinda lucky. Although, I've only used it in a gravel parking lot near my house to exercise the system. I've been "baselining" this thing for a year now and haven't even gotten off the pavement.
I intend to purchase the shaft that Toyotology is selling and get it installed with new brakes and any wheel bearings that need replacing. I hope the spindle is in decent shape...