[Station X]

Visual inspection of the chassis shows that the centre point of the capacitors is wired to a SIGNAL earth terminal which is insulated from the chassis. This is quite clear on the Trader sheet, but less clear on the manufacturer's sheet.

So with no earth connected and all things being equal there will be about 120VAC across each cap. With a good earth connected there will be full mains voltage across one cap and a low voltage across the other.

I take your point about leakage current. I'll pick up a couple of 10NF Y2 caps from Maplin. They're made by Wima and being physically smaller than the 100NF types will be easier to fit.