We had an issue with my wifes Jeep.
It is white and after it was washed, there were lots of dirty ingrained marks.
It is 2.5 years old.
I spent an hour or so with insect remover and one of the solutions to remove brake dust from the paint even then there were still some marks left.
The next day I used the insect remover again and all the marks were gone as the marks were now softer and were easy to remove.
I then used this two pack ceramic coating as used by proffesional detailers.
Probably took three or four hours to apply both coats.
The cars now cleans with no dirty marks remaining.
The ceramic coating was arouns ¬£10. This is what I used.Ceramic Coating Kit