That's an interesting theory which definitely holds merit. However I would look at that specific issue as a contributory factor, but perhaps not as a primary cause. Otherwise, how would you explain the 606's that don't have air bubbles?

One explanation could be a weaker return spring in some of the lift pumps so there is slightly less depressurization occurring with each pulse - but I seriously doubt that.

If the normal vacuum pulses in a properly operating system is causing the fuel to be juuusssst barely below the out-gassing threshold, then any additional resistance to flow on the inlet side could theoretically push it over the edge.

So... maybe the fuel tank screen being partially plugged and adding restriction at higher flow rates could be the culprit? I don't know... just an idea.

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.