I don't have an s2 pro, but an s3. And since I have owned it, I've replaced the stock throttle/brake servo, replaced the stock screws with stainless steel ones, and replaced the pull start cable with the rip master stuff, and replaced the silicone exhaust hose with one of these http://item.mobileweb.ebay.co.uk/viewitem?itemId=130811704566&kw=130811704566
And these also
http://item.mobileweb.ebay.co.uk/viewitem?itemId=160789824003&index=0&nav=SEARCH&nid=49436909067