thanks Georg and Klaus for your info. My unit is very new and when I slightly tighten the nut on the head, the slippage occurs against the motor, you can hear it winding as it slips. So my preference is to back off the nut tightening (return it factory default as I received it) and counterbalance. It may not be pretty but it works.
The canon nodal on the 16-35 is around the red ring so that particular lens is a problem. Not really very usable at the 16mm position other than a 1 row pano which you can almost do without the panogear.
I would like to try a 24mm 1.4L but again it's a heavy lens in combo with the 5D... but I would imagine the camera position would be much more centered. Anyone have experience with the 24mm or 35mm L-primes? I will be testing a 100mm with tripod collar in a week, hope that no counter-balancing will be necessary.
sorry for insisting ;-) just wanna be sure: may it be possible you shoot an image of your closed head and that you mark on the image the part which you did tighten?
(if its the wrong of two possible choices it explains your description and if its the correct choice than I would strong suggest you give the new head back to shop!)
and yes of course - tighten the nut so you can hear the winding or even worse that moving gets blocked is the most worst case and can damage the head - so loosing the nut again is not the badest idea ;-) ...