What you are expecting is them to potentially take ownership and accept a problem that very well could be caused by an install as the their own.
A jeep, more so a wheeled custom jeep is a maintenance whore and a challenge to keep in top shape.
The design..is on other rigs and proven
The execution and installation..done 3rd party and proven to have issues is done on your end and by your shop..I would start there and stop asking Genright to pay to have your undercarriage detailed and decreased.
You chose the axles
You chose Genright
You chose the shop that installed them that you are providing protection too, likely because they would drop you as a customer. I am guessing you are a challenging customer.
Who welded the diff cover? While it is a thicker cover, I cant say it would be my choice what so ever even before welding to it if I planned on it seeing rocks.
If your shop of choice welded that cover, you seriously may be a huge asshole pointing the finger in the wrong direction.
Figure that cover out first.
Take it off and have a machinist verify its not a warped pile of poo...then ask someone else to seal it.