[sdiy] black flaky chip legs: what does this indicate?

[Kenny Balys]

I completed a repair and had two 74LS138's with blackened
legs. I went to pull one and it came apart. The legs are
degraded somehow. Then on to the other 74LS138: same.
The legs of the IC's just fell away.

What could have caused this?
Has anyone seen something like this?

There is no Varta battery pack on the board. I have seen
something like this on a Poly-Six.

Other IC's near these two were not the same. The circuit
board seems to be ok.

The instrument is now functional after replacing the
two 138's and changing a few caps.

Thanks in advance for any ideas.