I've cracked it!
I have to thank a guy on another forum for the idea. I went to find the other half's nail varnish remover but unfortunately it said, 'Acetone Free', but I thought, 'what the hell'.
I also thought that de-mineralised water might help as we have very hard water here and that is not going to help.
Anyway, I painted the PA onto the back panel (pictured below) and left the central groove as a PA contol. I then used a kitchen sponge cloth thingy to wipe the left side with 'Acetone' and the right side with the de-min water.
As you can see the left side (Acetone) has a much cleaner, steely look while the right hand side (de-min water) has an ever so slightly brown tinge, no where near as bad as the tap water I was using.
As an after treatment I'll wipe/brush the area with the most volatile solvent I have, which is Lacquer Thinner, to make sure it is properly degreased.