This is a well known and long known Freightliner issue. My 2012 Dutch Star and now 2016 Dutch Star had this issue. The good news is now there is a fix without making your own shield, but it does cost money.
Recalls are focused on safety related issues. Freightliner has long known about the "dust storm" and views it as a nuisance issue. In 2012 I demonstrated the effect to a couple Freightliner engineers in Gaffney
. I am surprised with the all often complaint raised by mechanical-drive side radiator XC chassis owners, the dust shield or a redesigned fan shroud have not become the standard. Now that I have seen and driven the Spartan chassis based coach (K2 and K3) I noticed significantly less cooling fan "blow-by" on the Spartan chassis.
Also remember the RV industry standard, similar in many ways to buses, boats and aviation, and dissimilar to automobiles (with exception of tire and batteries) is your warranty is with the component manufacturer and not the RV manufacturer. This is why your motorhome came with a Freightliner label behind the seat and separate warranty paperwork. I don't see many RV dealers capable of working on a diesel chassis and at the same time, I wouldn't want most chassis shops working on the wood trim in my coach. Clearly an imperfect world, but easier once you understand the demarcation.