The crown of your collection, specially because it’s complete. Not every guy has redlines in his collection. They are called redlines because of the red lines in the tires, duh. They are the first models made by hot wheels (1968-1975 I think) and are very sought after. Google up to find more info.
Whatever you do, don’t touch it. Restoring redlines in a proper way is very complex, difficult and pretty expensive too. Besides, it was your grandfather’s. Keep it as is, don’t destroy its history. Think that it was your grandpa who gave it its current shape, and for surviving that it’s something of a hero.
You’d be better off finding another one in better condition, the Mark V is one of the easiest redlines to come by in that color, and they are amongst the cheapest redlines you can buy. 10 -15 dollars should net you one in near mint condition in the same Spectraflame green color. Hit E-Bay and see for yerself.