Actually it's more than just "applying some lubrication."
If you're going to do the service for your car, be sure to get the tech service sheets for the appropriate work. These cars are a bit esoteric and not exactly "normal." In the end it's up to you, but I'm personally happier doing it the way the MB engineers intended.
The proper lube is Spezial-Gleitmittel fur Glasschiebedacher. It comes in a 30 ml (1 fl oz) container, and is expensive but that 30 ml will last the lifetime of the car. If you're on good terms with your dealer you could ask them to do it. It only requires a few drops in the correct places, DO NOT over lube all the parts with just "some lubrication."
Mercedes-Benz Gleitpaste part number 001 989 14 51: "rail grease specified." (you might check on that part number, I'm not 100% sure on it but that's what I have in my notes from the dealer.)
Here is a pic from the service sheet. I'd buy the MB service sheets and/or get a subscription to STAR Tekinfo if you are truly interested in doing the service yourself, and doing it correctly.
http://www.startekinfo.com/StarTek/