The McLaren junior driver had his championship lead slashed when his Saturday victory was taken away hours after the race.
Sources at Renault Sport have explained to AUTOSPORT that what DAMS considered a simple painting process in fact included a layer of resin under the paint which reduced the curve in the DRS flap on the top side.
This addition of resin also increased the stiffness of the flap, to the point where it was much stiffer than a brand new version of the part would be.
It is understood that by reducing the flexibility of the DRS flap, which unlike in Formula 1 closes the wing off rather than creating a gap in the middle, it is possible to create a stronger seal that could give a slight increase in top speed when the wing is under high pressure.
While Renault Sport has confirmed that it did exchange several emails with DAMS about the possibility of painting the DRS flap (most teams use stickers), it has disputed the team's claim that adding the extra layer of resin is part of the normal painting process.
The rules breach did give race officials the opportunity to exclude Magnussen from the rest of the Paul Ricard meeting, but it was decided that exclusion from race one was enough of a penalty and the car will be allowed to race with a conforming DRS flap on Sunday.
It is also understood that DAMS had not failed a DRS check in the past because it is a random test that is only performed on the leading cars after certain races, and up to this point one of the French team's cars had - by chance - not finished in a top position in any of the races where the officials had decided to check the DRS.
The 2015 Formula Renault 3.5 season will be notable for being the last with the French company's backing but also produced a worthy champion in Oliver Rowland. PETER MILLS evaluates this year's crop of drivers
Last year's field was extraordinary and hard to match, but the Formula Renault 3.5 grid will still have plenty of talent this season. Glenn Freeman runs through the field ahead of this weekend's season opener
Landing the Fortec seat that took rising star Robin Frijns to the 2012 FR3.5 title was already a good sign for Stoffel Vandoorne. Then McLaren took him under its wing. Peter Mills tells Vandoorne's story so far