Hi Kevin,
It's only 'cause you Africanis are the worst cricket players in the world I have decided to come to your aid..
Some left field thinking..
1 Have you assembled your master cyclinder correctly? If you haven't done anything new to it, it's not the problem. Move on.
2 Here's a tedious plan but should help identify the culprit. Make up some brake line plugs to stop fluid going into calipers. Block off three calipers and bleed the one remaining until all the air is out of it. Move onto the the next one keeping the remaing unbled ones blocked off. repeat the excercise until you bleed each one in succession.
3 Finally bleed all of them collectively as normal.
If you're not successful, send me a return air fare and I 'll help you out.
BTW. I once put an entire new rubber kit through a 105 brake system and used silicon based brake fluid with the idea that this stuff is not hygroscopic and the system will not be prone to corrosion as they usually are. It also has a high boiling point so one thinks, bonus! Bad move, two months later, I had to strip it all down, flush clean everything, fit new rubbers again and use a regular brake fluid.
Why, because all the rubbers swelled up and my caliper pistons would not return once the brakes were applied. Sort of OK if you need a permanent four wheel hand brake on..
Er.. I was little pissed off having got this advice from gurus at the time. I trust you are not using silicon brake fluid?