As you can see in some of the pictures the paint on the Impuls Sport was beginning to come off in places leaving the clear body shell (look just below the "Graupner" decal) so I decided it was time for a repaint.
I had read in one of the forums that "De-Solv-It Graffiti clean up" was good for taking paint off a polycarbonate body so I purchased a tin from Amazon.co.uk. In the article in the forum suggested to spray on the cleaner and leave it for 10 - 15 minutes. I found that this wasn't really long enough. On the second go I sprayed the entire body shell and left the cleaner on for about an hour. The old paint then just washed off with warm soapy water. A few of the corners took a bit of scraping with a fingernail to get the last stubborn bits off.
A final washdown and dry with kitchen roll and the body was ready to go. I masked off the windows with ordinary masking tape and then started spraying the inside of the body with Tamiya Color PS46 (Purple & Green iridescent. It took many coats and the whole tin to paint the body (in the pictures below, the body has had about 3 coats).
Finally 3 coats of Tamiya Color PS 5 (Black) were applied.
I have ordered new decals to stick on but they haven't arrived yet.
Update - 9th November 2016 - The decals have arrived!