So, it's back on the car now - what did I do?
When a good proportion of the fluid was out I filled it with brake cleaner, left it overnight and then inverted it, left it for a weekend.
So much fluid came out, it was everywhere.
I then drilled both holes out to 8.5mm and tapped them to M10
Acquired some M10 copper washers and started the refill procedure, clear 100,000cst fluid.
I had to refill it 3 times and that small funnel took two hours to flow into the vcu, I was in no rush.
Eventually it overflowed out of the other hole after being left a couple of evenings. Took the funnel out, laid it on its side and let a little flow back out so that there would be air in there.
Acquired some GKN bearings:
Fitted them and dremel'd some M10 bolts up, one of the threads I cut not quite straight but that's what the copper washers were for, they allowed my brute attack with a drill to be corrected:
All ready to go back on the car.
The M10's will allow me to service it again in a month or so once the fluid has had time to scrape out the existing crud in there
I've refitted it but ran out of time before I could take it on a test drive. It needs a week of commuting I think before I do the one wheel up test - if it proves a bit stiff I can take the bolts out still on the car, drain a little fluid and then retest.