Erik - following is my recent experience with xenons.
Firstly i agree with 'drdj'. Go for bosch aftermarket ones which will cost you about half the price of mercedes ones which are the same thing - that's what i did. Only external difference (for hawk-eyes only) is that on bosch lights there is no tiny 'mercedes star' logo on glass (very-very small detail for one to notice even when looking up close, but that's how i got my username from).
Anyhow, took the dealer 90 mins to install/adjust - i also changed the high-beam bulbs to philips bluevision H-1 to avoid the yellowish look of the parking lights.
Furthermore, when i put on the high beams, the xenon low beams go off. The dealer said that in latest SL'S (1999 onwards) the low beams stay on as well. He also said he could do it in my car by by-passing couple of wires/switches etc, however he did not recommend this because in my original wiring the lights work through the ECU, whereas if he made it for both high/low beams to be on, he would have to by-pass the ECU - which he did not recommend.
Another thing is that the switch (which you roll up-down 0-1-2-3) by the headlights main switch inside the cabin becomes inoperable since the aftermarket xenons are adjusted 'once-and-for-all' upon installation and you do not have the option to lower your lights when the car is loaded / car's trim is changed. but to me this is not important, since a 3rd passenger never rides along (just me and my wife) plus that we don't load the SL with heavy baggage.
Hope above assists.
George
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