Lets see, at 40 mpg over 300,000 miles that's about $150? Seems a bit low for that many miles. I would wager it cost you more.
I would also wager that the fuel pumps were not as frequent or as bad from standard diesel fuel as your statement implied.
It would be clear that we should all use additive if the big rig fleet owners routinely used additive, which apparently they don't. The big rigs go for a couple of million miles I hear. Also, when ULSD came out, it was clearly stated that prior to that, quality of diesel fuel was not as high overall/average.
Sorry, I'm still on my first fuel pump at 173,000 miles for the CDI. My 2002 NB TDI was sold with its original fuel pump at 156,000 miles. Anecdotal yes. Strategy: use brand name fuel for better additives. Don't trust aftermarket additives for their ability to mix with different quality of fuel and different additives already in the fuel. Don't trust aftermarket additives that have no data nor offer any hint as to their ingredients, and their sales pitches are not precise enough to know if the benefits are infinitesimal.
Cheers.
TM