[Elecraft] Frequency shift in old K2

[Tim Pettibone]

For awhile, I've been experiencing a down shift of about 200 hertz, but
rarely and randomly in my K2 serial 0063.  It's enough to change the
characteristic tone in the receiver and degrades from the filter settings.
Any suggestions as to where to start looking?  Doesn't seem to be
temperature-dependent but I could be wrong.  And it, randomly, shifts back
as well.  Thanks.

Tim K5OI
Ruidoso, NM