I resealed the rear caliper again and all seemed fine when I fitted it.

Now it looks wet again! Could be residue from bleeding but I don't think it is. The caliper now seems it is leaking from the bolts that clamp the 2 halves together.

There are o-rings at the bolt joints, aren't there? Did you put them in?

Yes. 1 top & 1 bottom

Were the 'o'rings new and the right size,not normal to get a leak here ,are the joining faces nice and flat and free from marks or dings?

Or maybe they got pinched, or some dirt got stuck inside? I guess you're stuck splitting it again.