the power cable of the wheelbase has six wires going in
.. but that is for DC current between power supply and wheelbase.
Those DC lines presumably have substantial capacitors with very low impedance.
When I ground my rig, it goes away, only AC 0,78 V is left.
I do not know what is used for Fluke's ground reference;
properly grounding the rig should have reduced voltage to nearly 0.
I suppose that the cable between power supply and wall socket is 3 conductor,
and EMI filter would presumably be encapsulated in that power supply.
that should be right, right?
If there is indeed an EMI filter with capacitive voltage divider
and capacitors were exactly matched (very rare for capacitors),
then an ungrounded chassis voltage measurement with infinite impedance
would have been 115VAC in countries with 230VAC domestic supplies.
The Fluke 123 has 1 megOhm impedance rating;
dropping 115 to 8.55V suggests about 12.5 megOhm capacitor impedance,
ignoring phase shift, for 9.2 microAmpere leakage current. Your measurement is roughly 9x that,
but 0.78VAC measurement with grounded rig raises doubts about measurement conditions.
Regardless, 83 microAmperes is benign.