PTS 160 TCXO distorted sine wave output

[wd5jfr]

This PTS 160 (160 MHz synthesized freq gen) is intermittent and I think it's due to the 10 MHz TCXO output.  Sometimes I get a nice smooth output and other times it's distorted and later dies.  I thought it might be my scope or probe but another scope and probe show the same.  I kind of remember seeing a similar waveform on my Collins R389 PTO output.  I can't see the label on the TCXO can since it's right against the side panel.  Any ideas on the cause of this distortion?
Thanks Hank

[wd5jfr]

Anyone know what kind of simple circuit would output such a distorted wave from a symmetrical sine wave?