Hey LagDan,
I may just end up doing the exact same thing but still not sure the siren is the problem or the only problem, I just don't know enough about the car yet to feel positive, we've only had it a month. Once you installed the new one did everything work properly? What MB part number did you use? BTW, I grew up in Farnham and spent a lot of time in Bedford and Cowansville and I actually in Frelighsburg and Dunham last weekend just driving around.
Thanks