Cannot say specifically for the 156 but the normal way of retaining the handle is with a simple wire 'C' clip at the back of the handle around the shaft.
The clip is inside two grooves in the handle moulding but the ears should be protruding enough to get a trim removal tool on or possibly a pair of thin-nosed pliers. I have even used a thin screwdriver levering off one side at a time. You might not be able to see anything but you need to press the trim back around the handle and see or feel with a screwdriver if the clip is there. The open side of the clip is normally in line with the lever arm of the handle.
Hope it helps - at least until a 156 owner can comment.
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