Differential Unit problems of the 2009 Ford Mustang

The rear differential on my car was leaking fluid with less than 30,000 miles on the car. The 3 year/36,000 mile warranty had expired so I inspected it myself. When I removed the fill plug in the rearend I heard pressure escape. That told me the pressure relieve valve in the rearend was defective. But because of that my seals need to be replaced in my rear differential now. After talking to other Mustang owners I have been told this is a common and expensive and dangerous problem. This could cause fluid to leak onto rear brakes or even worse to much fluid lose would cause the rear differential to lock up and cause a accident. I modified the relief valve to fix the pressure build up problem. But now need to have the seals replaced which is a expensive repair. I rarely drive my car and it is always garaged. That is how I noticed it was leaking after seeing a puddle on the floor. I also know this is a common problem on that year Mustang because I've seen on automotive blogs on this problem and they recommend buying a aftermarket relief valve before this problem happens. It isn't like my car was driven in harsh conditions or even driven daily. I fixed the relief valve myself and have not had the damaged seal replaced yet,because I was going to have it done when they replaced the recalled airbags. Every time I try to set up a appointment they say the still don't have the replacement airbags in stock. I rarely drive the car now because of the issues and maybe driven the car a few times in the past 2 years. I believe this is a common problem on the 2005-2009 Ford Mustang and Ford should repair and replace any parts damaged by this issue. The relief valve is only a 10-15 dollar part but it's failure can cause thousands of dollars in damage and also a deadly crash.