I had a similar problem when I swapped a Westy roof onto my Syncro. The donor roof H-bar looked okay from the outside, but the guy doing the work (Ady at Boxwagen) took it apart to check, because he'd seen so many of them fail. There was a groove worn almost half-way through the shaft, so it was welded up, ground clean, and the job's done. The problem doesn't really show itself until the damage is done - luckily it's fairly easy to fix.
1990 2.1 DJ Syncro Caravelle/Westfalia conversion RHD