I ran a couple of tests - I put in the following capacitors (polypro 100VDC), and scoped the oscillations at 0TR1 collector
No capacitor - medium oscillations
10nf - bad oscillations
22nF - bad oscillations
47nF - medium oscillations
100nF - slightly less oscillations than no capacitor.
220nF - no improvemnt over the 100nF
I left the 100nF installed.
Other members advised me that they also don't have a capacitor there.
I'm going to hazard a guess that the capacitors were present on the early production units with the older square-type transistor, and when (on later production units) there was an Engineering change to the 2N3055, the capacitor was no longer required.
Learn from the mistakes of others - you'll not live long enough to make them all yourself!