The OM603 3.0 is a million mile engine.
The OM603 3.5 has been given the nickname "rob bender" in the US from it massive issues with bent rods thus ovals get out the cylinders and eventually total engine failure! This was seen in the US TD passenger cars of the early to mid 90's. Mercedes never did a formal recall but many who pushed at dealerships got new motors under warranty. Failure was seen between 70-150k miles.
Other issue early on with the 3.5 was with the #18 head and earlier. Too thin in places, over heating, blown head gaskets etc
As far as my truck...
I checked it out over a month ago, top to bottom and the spent weeks Googling and researching the 3.5l motor.
Basically, because this truck is a euro spec (vs US), a Worker model (not many made) and last year of production, they finally got it right. This truck has the newest head #22, upgraded thicker rods, newest head gasket design etc. As well, it seems that the euro spec'd cars did not have all the issues of the US cars. Some claim due to cetane levels others claim this and that.
It has 300,000 km on it and I am confident that it will be good for about a million miles like its smaller 3.0 older brother.
Here is an interior shot that shows its Worker heritage (similar to PUR)
You can see cloth interior, no carpet and truck was originally Polar White. It was painted yellow by Rega for SAR duty. While it has no burled walnut, the inserts are wood I am to,d but painted a flat dark grey.
It has 3 diff locks, a split rear bumper setup for towing, front has the tow pin steel bumper and no stupid body skirting like on the newer G500/550 models even though they are both 463 models

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Under the rubber floor mats the floors look new. Here is the rear cargo area:

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Luxuries include 4 speed auto, power windows, remote door locks, abs (can turn it off with a switch), ps, pb, and a driver side air bag. The 350GDT was the last model with mechanical IP. The G300TD (463) switched to electronic controlled IP and tranny
Anyways, it should be fun and in 5 years it US legal for import

Oh and if something should ever happen EVERYTHING on this truck is good for a direct OM606a to be dropped in and bolted up. Oil pan, T case, correct axle ratios etc etc... but that not going to be needed (knocks on wood)