5 months, it stopped working apparently. Won't extend anymore.
I don't know what is wrong yet as I'm about 1000 miles from it, but I suspect the rubber tube has failed as it is the 'weak link' in this system.
I'll be back in the same state again with it in a week or so and then I can give a full post-mortem.
<EDIT> Post mortem.
The hose failed at the attachment point on the top. This caused the rubber to snap down and collect at the bottom, which prevented the mast from retracting fully. That was rather inconvenient...
I removed the hose and held it up when we needed to extend it with the pin holes originally designed for this.
Since I'm now back to a single length of mast anyway, I've decided to go simple and use threaded rod and a DC motor.
That build is in progress.