Where these people using dot4 because they had a dot4 system though?

No, of course not.

Although methylated spirits works just as well to flush DoT3 & 4 brake fluid, for anyone who doesn't wish to deplete their drinks cupboard.

ken

On a side note, wouldn't it be great if meths tasted as good as it smelled?

and those white fire lighters give me a almost compulsive need to bite them

And I thought it was just me!

What size orings are in the rear wheel cylinders (LHM 16 mm)? I bought 11x2,5 and 10,6x2,7, I think the latter will be better suited? Ideal would be 10,8 or 11 x 2,7, but I couldn't get those.

Saurus,
it seems quite difficult to measure them accurately, but the O rings in the kits made by Wrakynson look to be around 11 x 2.5.
They will slip easily inside the cylinder when loose, but since the recess in the piston has a minimum diameter of 12mm, their overall diameter is 'around' 16.4mm once fitted onto a piston.

ken

p.s. Have you managed to get hold of replacement seals for the calipers?

Allright then, I'll try to measure them when I have the pistons out.
I ordered new caliper seals, together with a new LHM master cylinder because I couldn't take the pistons out without using "lethal force". And I'm not sure I'd trust a master cylinder which already destroyed one seal, maybe machining was off a bit and the gap was too big, allowing the seal to be caught in between when pressure was applied (this happens with orings if there is too large a gap left, so maybe it was the same here).
I already flushed the lines. First blew through them with air, then alcohol, then air again. This is what I used for pumping alcohol

Genius