I removed a splitter from the front of my 'new to me' BMW as it was ridiculously low! I had an awful job getting it off as it was factory fitted with some sort of bitumastic (I think) glue and took me two days with a hairdryer and lots of patience to remove it. Now I can't seem to sand it down to a fine enough finish to spray it. There still seems to be black glue (rubbery stuff) that won't rub down and I tried filler but it looks awful. I am considering using some stonechip type paint and then spray/lacquer it but don't want it to look cheap and nasty. Any ideas please?