John ,
I have never used it, but ultrapac has worked well for me both on draught marks and soot marking.
I am tackling a job on tuesday , filtration marks all along the edges were the fitter has been too heavy handed.
Explained to custy the reasons, charge a little extra and dont promise the world.
Most importantly, explain the possibility of them returning over a period of time, unless the cause is of the problem is rectified.
Geoff