Is His RPT a LCD model or a CRT? If it is the latter He may find that one of the mirrors that reflect the image from the 3 CRT guns are out of line of that one of the guns(RED,GREEN AND BLUE) is not functioning properly. I also believe that the LCD models also use mirrors to get the image onto the screen.
It is along time since I personally had a Rear-Pro TV, Mine was a 40"" Tosh which used the 3 Gun system and when one of them died is was a better option to start again rather that have it fixed, and there was the start of my happy tale with Plasma!
Tell your friend to bit the bullet and Lob the old Rear-Pro and start enjoying Daytime Viewing and come to think of it a much wider viewing angle and get a Plasma.