Lincoln MKX 2013 Front Bumper Mystery

I purchased a certified 2013 Lincoln MKX on 9/14/15.

I noticed cracks in the front bumper 2 weeks after purchasing this car. The front bumper has been replaced 4 times since and is still cracking/melting in the same area.

The dealership attempted to diagnose the problem once but was not successful. With no other explanation, I was informed that it was an external cause and that I was probably parking my car above a heat source causing these cracks.
After the 3rd time I contacted Lincoln and sent pictures of the bumper. Just by looking at the picture, their engineers said it has to be from outside source, such as sun reflection from a window. I reassured them that was not the case and that I park my car in the driveway, and at work I park in an open field. They also said if it was an internal heat source, I would have lots of electrical problems.

I am devastated because I know something internally maybe causing the cracks and no one seems to help. On several occasions I’ve noticed the front passenger side of bumper hot to touch. The car currently has 24,000 miles. The car drives good, and I don’t smell anything unusual.

The only other repair was a steering wheel was replaced by the dealer because of the leather cracking.

Could it be an structural damage, or other issues such as manifold gasket?

Appreciate your help.