I have a 2004 SL 500. The alarm Siren goes off on its own, while driving and also sitting and turned off. At first I thought it was the service battery, how ever after charging it (it's only 18 months old), the siren still sounds sporadically while driving. The dealer said I needed the alarm replaced at a cost of $395.00 for parts and one hour labor. Could anyone please tell me where this item is located so that I can replace it myself. Thank you.