2000 Ford Explorer Transmission Trouble

My 2000 Ford Explorer recently had the valve body gasket fail on the transmission, is this common? What would make it fail? I read in another post that it is not unusual because of a possible design flaw. Any help on this subject would be appreciated.
This vehicle only has 47000 miles and has also had the head gasket replaced, new front brakes, new ball joints, new drive shaft and a few other problems.

Thanks,

Bart