Diesel

you can not rebuild a commonrail pump your self. they need new internals as they damage with any form of dirt or moisture . and are way higher pressure then the old rotary pumps. I dont like commonrail crap and got me a unit injector tdi vw . now they are even more easy to fix then any other diesel. cost of parts is a differnt story but you only got 4 injectors they are the pumps and injecors in 1 unit and 2 fuelpumps to worry about one in tank and one on side of engine that is part of the feed pump for the pumpedüse and is also the vaccume pump.

now the problem is not only the CR pump on new diesel its the injectors and the egr system to worry and maintain also correctly, failing to do this = tousends and tousends in repairs worst case will be . premature worn injectors client neglects or cant hear its not running right and one of the injectors sprays out of alignment not in to the piston mould where new direct injected diesel have to spray and burns a nice wee hole in the piston and now it realy runs rough with 1 pot having 0 compression. That is the (worst case of what ulsd diesel) is capable off

you might now say pumpedüse cant be that good since vw no longer fit unit injectors and use now cr-common-rail pumps to there engines. yes that is correct the reason for this is however only 1 and that is the greenies.
The pumpedüse are inside the engine and need a special cooler to cool the fuel down cooler is under the car bolted to the floor . the problem is euro 4 , 5and 6 emissions to get to euro 4 egr systems and particular filter where fitted that cause all extra stress and heatbuildup, So the unitinjector was unable to cope with that and you do get worn out camshafts , and i recon the problem is the heat destroyed the lubrication oil film when there is a slightest problem with egr system. commonrail tolerate more heat as the diesel is not mostly inside the engine and has little more ways to cool down in the rail outside the engine etc. But they are not immune to egr faults and also destruct if the egr system is not stripped cleaned and maintained at imens cost to owners of these vehicles.