i have a 1990 190e and the paint still has a fantastic shine,this might be due to the amount of polish I have applied over the years,
If I was in your position I would first claybar the roof, then use a good grade polish, preferable black, polish it a number of times,
I would suggest using a buffer and some G3 but you need experience to not burn the paint. wax on wax off,should make a vast improvement.