don't think DU has been used in civil aircraft .. although a post accident problem from time to time with military
The B747-100 series aircraft had DU mass balance weights on the rudders/elevators and outbd ailerons, (I'm not entirely sure but it may have been replaced by Tungsten in the latter years on some fleets) also the JT9d engines had DU in the nose cowl on the outbd engines (can't remember why but I think it was to damp out 'pod nod') this was later replaced with a big lump of tungsten in the end of the exhaust cone on all engine positions that had the same effect and also 'detuned' the natural resonance.
The DU used to be inspected for corrosion and paint damage.
It did become something of an issue after the loss of PanAM 103 when the NRPB got all excited and there was a problem in finding out how many weights were fitted and where.