Ok, I'll post. I'm curious to see what you do.
The factory paint job on a T1N Sprinter is terrible. My roof is awful, the original owner left it out in the southern California sun for 11 years. The second owner was going to put Monstaliner on the roof, he had the body touched up in areas. I considered it but the roof leaked so bad I spent months finding all of the areas water was getting in. I don't like the texture of typical bedliner and got a sample of the smoother liner but couldn't figure how to paint something that high and was worried it wouldn't last long.
About 2 years ago I got a $5K quote to repaint only the the roof, they said their paint job would last 5 years. I bought rattle can automotive paint, removed all the rust I could from the gutters and primed and painted. I'm not that great at spray can painting but it looks better than the rust and I spent about $100. I still have some rust spots on the roof I'm thinking of spraying. I will have to do something better in the future because I have 2 areas I can't fix. I would like to repaint the whole thing but worry the cost would be too high.
Your situation may be easier because you aren't dealing with rust. I should put more effort into getting quotes but I get tired of the outrageous quotes and condescension. I really don't want to go to Mexico to get it repainted either which is a common suggestion.