Originally Posted by
spclark
That's a 1989 steel framed Panasonic? I'd like to know more about its history over the 36 years since fabrication, what condition the rest of the frame components were in once that damage became evident.
In the pic I see rust migrated through paint at the juncture of the seat tube / down tube / chain stay join. Everything manmade fails in time.
That's a bulge-formed bottom bracket shell. Those often do not have direct tube/shell contact for the full depth of the tube socket, leaving a stress riser that can crack. I've repaired such a failure by cutting the shell into pieces, sweating off the pieces, and installing a new investment-cast shell. It's a big job, and not likely worth the expense unless you're doing the work yourself.
N.B. still riding the repaired frame 40+ years later.