This from a diesel web site.
Fatal Flaw 1: The Killer Dowel Pin
The first such weakness affects 5.9L Cummins engines manufactured between 1988 and 1998 (in other words, 12-valve Cummins engines used in Dodge Rams). These engines feature a steel dowel pin that locates the front timing gearcase. Over time, this steel dowel pin can wobble out due to the constant heat cycles and vibrations of the engine. If (or when) the dowel pin works its way completely out, it falls into the timing gearcase.

Read more: http://www.dieselpowermag.com/...l.html#ixzz2kxOjffVs

When the dowel pin falls, a few things can happen. If you're lucky, the pin will miss everything and just fall straight into the oil pan. If you're not so lucky, it will hit one of the timing gears and shoot out the side of the timing case, creating a BP-sized oil spill in your driveway. In the third and most unfortunate scenario, the steel pin will jam between the timing gears. This typically causes the cam to break, the valves to hit the pistons, and the engine to internally self-destruct. While this last scenario is rare (a hole in the timing gearcase and a big puddle of oil is most likely), it has happened to many unfortunate enthusiasts, which is how it got its name-the killer dowel pin
For a KDP repair, most of the front of the engine needs to be disassembled to gain access to the timing gearcase. The fan, shroud, overflow bottles, balancer, and lower pulley all need to be removed. With the front of the engine stripped, you can install a small metal tab over the dowel pin to keep it from rattling out. While you're in there, make sure to tighten up all the gearcase bolts. These bolts loosen over time and will do just as much damage (or more) if they fall into the front geartrain. Many diesel companies (such as TST Products and Source Automotive) sell killer dowel pin kits for about $60 and include a tab, timing cover gasket, and front crank seal to put the engine back together. After performing this repair (or getting a shop to do it for you) you'll feel much better knowing you're not driving a ticking time bomb down the highway.

Read more: http://www.dieselpowermag.com/...l.html#ixzz2kxNuYBdb

Read more: http://www.dieselpowermag.com/...l.html#ixzz2kxNTHevu

What have all you 5.9 owners to offer on this? Taking the front off the engine is beyond my expertise as are most other things. I contacted Cumming Cross Point in Knoxville and they said they sell about 40 of the repair kits every year.

I for one, am not going to loose any sleep over this. I have 205k miles on mine. If it fails, at this point I would just swap out the engine for a high output 6.7L Cummins.