Even 1 volt DC on a ceramic resonator is enough to induce metalisation
creep over the edge of the thinest element inside , given some time.
Being 40 years old and/or dampness/condensation can induce it also,
whether powered up or not, dissimilar metals and moisture providing the
"DC".
Easy job to remove them , well 3 pin ones anyway, and of course should
show no DVM-R reading