i'm planning to buy an aftermarket alarm system and starter immobilizer for this car.
any comments, potential problems? thanks for any advise.

Looking for an alarm, eh?
Buy a quality system - Clifford, DEI, or Avital (made by Clifford) are good choices. Even more important is finding an installer that has Mercedes experience - the vacuum operated locks on these cars can be tricky to wire into. My installer physically attached an electric switch to the lock post in the driver's door, thus circumventing the vacuum hassle.

I think the starter disable is not worth investing in. If someone wants your car they will get it. Soon I will be offering a keyless remote entry that will interface with your vacuum door lock pump and factory alarm and lock and arm both. Email me at Benzmac@peachparts.com and I will put you on the list.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM