Are you familiar at all with the PD fuel system?
Here's the TDIClub definition - which is pretty good:
"Other VW TDI models with the 1. 9 litre 4-cylinder of 115 hp or 150 hp, and the 1. 2 litre and 1. 4 litre 3-cylinder engines, use a so-called "pumpe-deuse" (German) or "pump-nozzle" (English translation) system. In these engines, each cylinder has its own small high-pressure fuel pump which is actuated by the same camshaft that operates the intake and exhaust valves. Fuel is delivered to each pump-nozzle by a low-pressure pump serving the same function as the internal vane pump in the distributor-type system. As the engine cylinder approaches the end of the compression stroke, the main pump plunger advances, pressurizing the fuel. A solenoid valve adjacent to each pump-nozzle is normally open and bypasses the fuel. When the solenoid valve is energized, the bypass passage is closed and the fuel is forced to an extremely high pressure and through the injection nozzle. At the end of the required injection period, the solenoid valve de-energizes and any remaining fuel pumped by the plunger bypasses the nozzle. Thus, fuel is injected as long as the solenoid is energized, allowing full control of injection timing and duration. This system has the significant advantage of eliminating the separate high-pressure fuel lines from the pump to the nozzle because it is all built into a single unit, thus giving better control of the injection cycle. "
These unit injectors are $400+ a pop - and they're kinda like the 7. 3/6. 0 PSD injectors. They're slightly easier to swap out in the VW compared to a PSD if something goes wrong, but it's still not a job I'd look forward to. (The 7. 3/6. 0 PSD's use high pressure engine oil to hydraulically actuate the injectors which are commanded with AC voltage to open/close - this has to be the one of the worst ideas I've ever had the misfortune of working on... )
I would say that the PD fuel system is LESS robust in terms of being able to withstand impurities in the fuel than even the problematic VP44 - pretty much all other fuel systems on a B-series are quite robust and a lot less simple. Other Cummins engines/fuel systems have a varied history and service record... CAPS. :-laf (Unit injection is stop-gap technology to get folks past the pump/distributor - nozzle approach and into the common-rail age. It provided higher injection pressures to clean up emissions, but it is problematic... )
Take the common-rail approach for example - the CP3 high pressure fuel pump does only that... make high pressure fuel... which is then distributed to the rail and then to each injector. Each injector is then commanded to open/close independently. The CP3 has no concept of timing and it couldn't really care. . it's an incredibly simple and highly effective fuel system... the complexity lies in the ECM - but it only needs a few variables obtained from sensors monitoring the operational characteristics of the engine to determine what to do.
With PD, you have 4 high pressure fuel pumps each built into a unit injector that is also being commanded to open/close independently - see where I'm going with this?
VE44, P7100 are very forgiving due to the lesser injection pressures involved. The VP44 isn't terribly forgiving and has some very tight tolerances inside, but I'd worry less about putting non-OEM recommended fuel additives through that pump than I would a PD. Besides, they're easier to change not to mention readily available - you can't say that for the PD fuel system.
My best advice for a PD owner would be to install a 2-micron fuel filter and add a little Power Service every so often.
It's not that the PD doesn't need extra lubrication - it does... I'd just use stuff that was designed specifically for a diesel fuel system. 2-stroke oil might work OK, but I wouldn't use it in anything but a 2-stroke.
On edit: I'm not defending the TDI Club by any stretch of the imagination. The majority of their members wouldn't even think for a second to do anything that isn't in their owner's manual... however the PD fuel system is expensive to repair and delicate... so they're being cautious... as I would be if I were asked to provide advice on one. I wouldn't own a PD engine and may not get a new TDI when they're common-rail... we'll see how VAG handles the new engine after it has arrived stateside and run around for a year or two.
Beers,
Matt