I'd say the sludge would most definitely be related to a bad batch of fuel as I've owned my R32 since 2001 and recently dropped an 044 intank. The tank was 100% clean an the cars now done a little over 260,000km's in total.
I've only ever ran BP with the occasional tank of Mobil and recently Shell as its only 10c more compared to BP of which seems to charge 13c more