Yes absolutely do the guide rails when you have the front timing cover off. Its not difficult and it'll extend the life of the chain.
My experience has been that even using the Genuine MB sealant doesn't make it leakproof for very long...you still end up with a fine "mist" of oil over the areas after 10-15k...

Victor-Reinz sucks, just avoid them aside from intake and exhaust gaskets...that's about the only gasket I've used from them that I didn't end up having to re-do.
Im about to re-do my valve stem seals after 80k as I am burning over 1qt per 4k miles.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k