I tried to provoke some debate on this at
http://www.pprune.org/forums/showthread.php?t=266124 , but failed! That was before the presence of silicone had been detected, though.
Well, I'm still concerned. In the same way that silicone wax can craze GRP, silicone oils can migrate into certain plastics and provoke brittleness and cracking. Just one insight to this is,
http://www.springerlink.com/content/n5g72817632813n8/ . I have an ex 3 Cdo 1/2 Ton Rover Truck that spent most of its Service life in Noggyland. The grease in the steering column had been replaced with silicone grease; you could tell from the feel. The bloke I bought it off had just replaced the Indcator switch assy. About 3 years later the unit fell part. The ABS moulded body had more cracks than a Bangkok brothel! I replaced it with the correct "arm and a leg" Lucas unit and, lo and behold, that too fell apart after just 4 years. I'd used MS33 grease in the past, for what it was intended for, and already noticed that the plasic cap on the tube never seemed to hold together for much over 2 years.
I know that my aeroplane has some reinforced PVC fuel lines and the exhaust vents directly into a GRP propellor. Maybe I'm paranoid but I'm glad that it's got AVGAS 80 in the tanks. As an aside, it does annoy me that CIVGAS/ULGAS (the supporting DEFSTANs have been cancelled, incidentally) is now adulterated with ethanol. I'm not normally inclined to fly at 6,000 + feet but I don't like having to worry about feed line vapour locks.