Timing Tensioner problems of the 1999 Ford Expedition

Approximately 2 weeks ago, I noticed a burning smell/oil leak in my 1999 Expedition. I promptly took it in to my mechanic to be diagnosed. It was determined that it had a leaking head gasket (this engine has only 46,000 miles on it, and the vehicle has been extremely well maintained). I spent many hours on the phone with Ford, but was told they would not help. Feeling stuck, I went ahead and authorized my mechanic to go ahead and fix the head gasket at our expense (of nearly $2000)! unfortunately, this nightmare only got worse! yesterday, my mechanic informed me that while tearing down the engine to get to the head gasket, he determined that the timing chain has worn clear into the guides/tensioners. He (and 2 other qualified mechanics) have stated that there is no explanation for this other than defective manufacturing. There is nothing I could have done to have caused this. The cost to repair this problem would be an additional $1500, now putting my total at nearly $3500! both the mechanic and I spent much of yesterday on the telephone (yet again) with Ford, but they are still refusing to take any responsibility for these faulty engines! it sickens me that they can charge $40,000 for a vehicle, then not be made to stand behind them! I have been absolutely amazed at how many other reports I am reading (here and elsewhere) about this very same problem occurring with the head gaskets. Why hasn't Ford been required to fix this problem? this Expedition was my "dream" car that I saved 2 years to buy. I cannot even begin to tell you how much that dream car has turned into a nightmare!! please make Ford take responsibility for these defective engines!!.