Issues of breakage with early versions of the Z1 have been fixed.
Make sure you get one of the newer models. I use a Wimberley Sidekick rarely with my Z1.
Predecessor had lockup problems, but seems like it has been fixed with Z1.
I had a B1 before until it was stolen. It was one of the latest series and I only had it for ~1 year. It never locked up. But I was on a tour with a friend as his B1g locked up.
I now have a Z1 for 1.5 years and use it very often. I have two isses with it:
1) The panorama plate has a screw, this one could under very rare conditions slip under the panorama tension mechanism. In this case, the panorama rotation (on the bottom) slips one or two degrees when tightening. I had a call with Arca, got an immediate help on the phone: open pano tension, move the pano mechanism very fast a few times so that the small screw gets out of the way of the tension.
2) In very cold conditions (-10°C/14°F) the ballhead could move rough. It is not that smooth any longer even if friction has been openend completely. I also had this issue with my B1. However, it does not lock up, its just that you need a little more power and it stops rougher.
Z1 could possibly rust if immersed in water. Or if living in a climate with salty air.
I never heard this before, but notice that this website talks about a B1. You should ask Precision Cameraworks directly!
Honestly, I think that choosing between BH55 and Z1 is like choosing beween Canon and Nikon. For me as a european I am sure I will never buy complex RRS products (like ballheads and tripods) again. Thought I own a BH40 and are very satisfied with it, there is no repair service in Europe. A friend's BH55 that required service is currently stucked in US customs since 1 month now as to current terror warnings. I know RRS is a small company, and how they started, but in the end our globalized world is sometime not-so-globalized at all.