My parents purchased the vehicle from a shop, which reconditioned the vehicle after it was totalled by the original owners. Several weeks after the purchase the transmission "exploded" while shifting out of park on the hill outside of our house. At the time I did not own the vehicle and I use the term "exploded" because I go only by the description provided by my brother and sister after the incident. However, the area outside of our house which might be called "ground zero" provided significant evidence of a detonation of destructive power. However, to be fair to the old girl, it was used for the first ten years of its life primarily as a mule for a 25 foot boat. Also, from what I have read the four speed automatic transmissions are prone to failure at mileage in excess of 100,000. The repair cost for a rebuilt transmission ran about $1,800 I believe.
My parents also replaced the passenger side radius arm bushing. I believe that cost about $200.
Since I was donated the vehicle by my parents in 2004, as a winter beater ('79 Firebird in the summer), several more things have failed.
The radius arm bushing on the driver side has deteriorated resulting in a "loose" feeling in the front end and a popping sound when the brakes are applied and released. This is caused by axle-wrap, which is annoying, yet not serious, and is nothing I will be paying to have fixed.
The four wheel drive is inoperable. Failure of the shifter motor on the transfer case is common due to a deteriorated internal stop gumming the connections. However, after removing this and rebuilding it myself I unfortunately determined that this was not the problem and instead the auto locking hubs were destroyed. Another item I will not be fixing. 4X4 does work if in dire need, however, it is not pretty.
Several other small common items have needed to be repaired or replaced since I have owned the vehicle:
Brakes: front and rear, entire exhaust system, starter (twice), a stuck thermostat, rusted transmission lines (in and out), and the oil pressure gauge failed (A few scary days until I resolved that it was just the oil pressure sending unit).
Also, there is the standard Ford Explorer copyrighted extreme rocker panel rust. Also a little rust on the roof and lip of the hood. However, the floors and wheel wells are surprisingly spotless.