re dashlights (reprise)

hi posted a while back about dash lights playing up, intermittently not lighting at start up. Finally got out the spanners and pulled the Voltage regulator, and
discovered that the brushes were fairly well worn, down to half an inch ( - 12mm) and grooved about 20 thou ( 0.5mm) deep and wide. Fortunately had a spare so dropped that in - instant cure! Thing is , I had a new (recon) alternator about a year ago - I was wondering if the grooves are due to an internal fault, misassembly or just wear - is this normal? Dont know that much about car electrics, most of my bikes had Lucas brushless alternators or 6V dynamos... Anyone seen this before? cheers balge
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