I've been putting off removing the undercoating from the rear wheel tubs because its such a nasty job but I finally started in on it yesterday. Small areas of the undercoating had fallen out over the years. This way I can seal and undercoat everything from the firewall back.
I used a $30 ebay needle scaler and if you haven't used one to remove undercoating, you really need to. It FLIES off....which is why its so messy!