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TQC Piston Failure

   I have a quick question/heads up for turbo owners.  Recently I was
experiencing some oil consumption, boost inconsistancies and high pressure
in my crank case.  A compression test checked out and I decide to take off
the head, spruce it up and replace a supect gasket. 
   It turns out that the # 5 piston was setting up to self destruct!  In
the area between the oil ring and the next (compression?) ring, the 1/8
inch surface area of the piston had begun to seprate from from the piston. 
A total of about 4 pieces, all about 1/8-1/16 long, and the depth of the
ring cut  were seperated fron the piston and free floating between the
rings!  Luckier still was that one of the rings had broken but not yet
fallen out and kept the pieces between the skirt and the piston (all pieces
present and accounted for). 
   Incredibly, the bore is clean with no scoring and no measurable signs of
taper or wear, i think new regular size piston will do the trick, luckily
no bad signs higher boost on the other pistons.  I have seen melted,
detonated and banged pistons, but never this failure mode, any ideas?. 
Better on the bench than the road I guess.  Another Audi repair set to
really exceed the estimate!