What many in this thread fail to realize is that not only do car companies under the same umbrella share parts.....different brands also use components from the same manufacturers.
Does anyone here actually understand the complexity of the modern vehicle?
I've been to the Automotive Testing Expo in Novi, MI and was astounded by the amount of sharing that goes on between brands. The auto industry is the most highly regulated and highly tested industry outside of the aviation field (thank goodness!). No manufacturer makes all of it's own parts. They not only share with other lines in their own line up but with other manufacturers as well. This helps keep costs in line and does away with the redundancy that would exist otherwise.