Andrew R Stewart 

Simplex did offer some of their lower cost parts in a white plastic. First time I saw one I initially thought that it was REALLY dried out, the black nylon will off gas (or so I have been told) and slowly loose the deep black. When I see this on repairs I apply oil to the surface. This makes it look better but the deeper color doesn't last long. At least with the imaged white ones the ft der body hasn't cracked at the seat tune clamping thread insert.

As to the broken quill wedge bolt (I think that is what was described) they do break although not a common issue. What is more often mentioned is the expanding bottom type of design (as opposed to the more common sliding on an angle design) can have two issues. One is that the steerer sees a very focused expanding force and the steerer can develop a bulge from the stem's being over tightened. The other is that the stem bottom is split into two halves that get spread by the conical wedge. These "halves" can crack and separate from the rest of the stem. Andy