It happened to me once with a Nikkor-S 50mm/1.4. The culprit was the lens release tab of my Nikon SP which had got unscrewed a bit and out of exact alignment wiith the small pin of the lens mount helical, so it didn't recess properly when I mounted the lens and as a result the lens barrel tab broke.
AFAIK there is no easy remedy. Soldering wouldn't work but for high temperature plumbing brazing which would make the barrel melt. Making another tab thanks to drilling the barrel and making something protrude from the inside of the barrel was the solution I thought of, but this didn't seem realistic to me eventually.
At the end of the day I neatly filed down the broken tab so that it couldn't harm my fingers and I decided to leave the lens as it was.
I just made the lens mount more tightly onto the camera thanks to that good old trick :
http://www3.telus.net/public/rpnchbck/loose%20inner%20lens%20mount.html
Since, the lens has been passed onto a friend (RFF member) for his Nikon S3 2000. He always told me that the lens was keeping mounted tight with no problem in daily use. Ditto for dismounting and mounting the lens again and again.