Distorted Sine Wave

Gentlemen,

Whilst fault-finding on my HP 8566B spectrum analyzer, I've found the
10Mhz reference oscillator is generating an 'unsatisfactory waveform'
which may be causing the device to be unable to lock it's main PLL.
I've come across this waveshape before, but mostly with oscillators I was
building and in the process of trying to iron out the wrinkles of and
certainly NOT a critical reference oscillator from a respected
manufacturer. Can anyone tell what's most likely going on here?

https://disk.yandex.com/i/z6fYbeVfPRK7aA