Just wanted to share my experience in repairing a 336...
A friends 336 30-30 would lock when the lever was fully cycled and not move. I told him I'd take a look. After doing the initial take-apart like you are going to clean it, I found nothing. So I had to take it all apart. First time and kinda scary, would I be able to put it back together? After taking it all apart, nothing was really noted. Cleaned all parts and I put it back together. Same problem. Took it apart again. This time I notice that the carrier rocker was very sharp and worn. Not fully knowing how this worked but thinking this may be hanging on things, I took a small file and removed the sharp edge. I reassemblied it and it now works fine.
So I have shown that even a blind monkey can get it right sometimes.
Good Shooting,
Deerandduck