Sanding down the rear bumper of the stone chip and then moving on to the sills, am I right in thinking it is removed with a heat gun and scrapper and how far under should I go, should I go right under to the edging

That's how I removed it from my sills. I went all the way as the paintshop were going to re do the stonechip underneath the sills and smooth the bit you can see.

Cheers

Get them nice and hot almost smoking and it scrapes off easily..

I might be wrong or worrying to much but id be scared heating it up my damage the paint inside the seals and start rusting from the inside,

Even if u spray cavity wax in there id still be happier for having the paint to protect inside too.

But im just a worrier when it comes to my zed and I hate rust its horrible stuff, and probably will be fine lol.