clean the dip tubes too. they might have cleaned the inside walls of the keg, but might have skipped the insides of the tubes.
if its a re-furb'd keg, ALL the o-rings were supposed to be replaced (2 dip tube, both post QD rings, and the keg lid o-ring)
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10