You could try caustic soda on a small edge to how that works. It cleans aluminum very good. Some alloys will turn black though (but are easy to be buffed to a high luster of silver again) Make sure to do it outside the house, DON'T inhale the fumes.. (don't use it on the purple parts, it will loose the color very quick :
My G1 is all purple - it was a race truck, so it has its scratches for sure. it actually hasn't been built/run in years, but is resting under a shelf with a Gorilla suspension installed. Last time I ran it, it had lexan mud guards and a 1/8 buggy body on it - looked like a wide 1/8 buggy. :-)
The G1 would look awesome with a buggy body on it! Good to know there is another purple G1 out there though. So far, I have only heard of 2 purple ones (yours & mine mike) 1 blue one, and 2 black ones... I have seen a silver one too, but do not know the owner... (I found it by googling Gorillamaxx G1)