Autoglym make a product that will clean off the silicon:
Intensive Tar Remover - Products - Autoglym
I believe the aluminium used on the Kirkham bodies is much higher quality than that used on the AC. The Kirkham bodies stand up well without any treatment on them. I polish mine once a year and then just use a vinegar type window cleaner to take off bugs and the inevitable finger prints.
I did a charity track day a few weeks ago taking paying passengers for laps around a circuit. It was very busy and as soon as one passenger was out, the next one was in. What I didn't realise was that people weren't taking care when taking off the harness and the buckles on the shoulder straps were bashing against the door top. I now have dozens of small dents and scratches in the aluminium.
I might look into putting a clear film on the tops of the doors. Has anyone tried this?
Paul