CASTROL PORSCHE 936?


Perhaps I'm a day late for April Fool but this raised one bushy eyebrow the other night. Ebay continues to offload PT-4000 sets by the bucket load and this one was mildly curious because it has GTX written across the back of the Porsche 936.
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Now, I immediately assume that someone has put the Castrol GTX logo from the crash barrier on the back of the Porsche but I have a nagging doubt that I have seen this done before.
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I'm just slightly curious that maybe there was a version like this? Can anyone confirm or am I just kidding myself?
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Maybe I've fallen foul of my own April Fool's joke?