The 2008 Sprinter was purchased new on 3-26-08 and sold on 11-9-14.  Spent about $20,000 for the conversion materials.  Drove the Sprinter for 57,000 miles.
There were three failures.
 At 10,000 miles I had the fuel filter changed by a local shop.  Local shop did not tighten the hose clamp on the intake hose feeding the turbocharger.  Van would not run so it was towed to a dealer.  Not Mercedes fault but a simple repair made into a major problem by the Sprinter computer.
 At 20,000 miles the EGR valve failed and Sprinter went into limp home mode.  This was a serious failure because the van lost power.  Problem occurred just after I had passed several cars on a two lane road.  If it had lost power just minutes before, the failure could have caused a serious accident.  At that time the decision was made to sell the vehicle.  Did not need to drive a vehicle that decides to reduce power whenever it wants.  At that point I lost confidence in the vehicle and was nervous about the Sprinter quitting a long way from a service center.
The last failure occured just before Sprinter was sold.  The Mercedes optional bastardized Espar heater failed.  The heater is designed to heat the engine water to help the diesel engine start in cold weather.  Mercedes removed the Espar controls and water pump and integrated the heater controls into the Sprinter computer.  First took van to a qualified Espar repair facility.  They removed heater and could not see anything wrong with the heater but could not repair it because it did not have the Espar controls.  Then took van to an authorized Sprinter repair center.  The dealer was not familiar with the heater and did not have any troubleshooting software to help determine the cause of the failure.  Service manager called Mercedes to obtain documentation on how to repair the heater.  Mercedes told him that they did not build the Sprinter (It had a Dodge nameplate) and they do not install heaters so it must have been installed by a third party.  I showed dealer my window sticker that listed the heater option and the Sprinter sales book that explained the option.  Service manager did not know who to believe.  After several months and many visits with no help from Mercedes, I found a new Sprinter on the sales lot that had the same option.  Led the service manager out to the new van and suggested he look at the exact same heater on the new van that I had on my van.  He was then convinced that Mercedes did supply the heater.  He never got help from Mercedes so he started replacing parts until heater ran.  My repair bill was about $2,000.00.  Not a proper way to treat a customer.
I bought the Sprinter because it was the only high roof van available.  Incorrectly thought it would be reliable because it was a Mercedes van built for commercial use.  My use as a travel van would not be a heavy duty use so thought van would be very reliable.  That was not the case.  Was not impressed with the vehicle's engineering.  Many very odd design choices.  The lack of service locations and high parts costs along with the reliability issues convinced me to sell the van when the high roof Transit became available.  In my opinion the Transit is a much better vehicle.  Prefer a gas engine instead of a diesel.
The Sprinter worked very well as a camper.  I had made the right choice for the layout.  The only change I made was to replace the 135 watt solar panel with a 205 watt panel.