Had to repair my Alternator on a 2001 CLK Kompressor

I bought this car, immaculate condition, full service history & it had
done 90,000 km for a 3 1/2 year old car. Anyways, last week, the
alternator failed & i had an electrical failure.. took it to my
mercedes guy who proceeded to tell me a new one would cost $2000
(australian for a new alternator) so he got it repaired for $600!
either or sounds expensive, and im shocked that the alternator failed
after just 3 1/2 years... 6 months outside of factory warranty.. can
anyone give advice, any way of getting mercedes to reimburse me, or is
it just BAD luck?