Are you sure it's the actual bottle that is leaking? It's more likely to be one of the various hose connections - weak point on the e-class is the plastic connector on the headlamp washers (if you have them). You'll probably see a pool of water under either front side of the car if this is the case.
MB Stealer quoted me £120 recently to replace this headlamp wash connector .....the entire front bumper has to be removed to gain access .
Anyway, if it is the bottle then you need to remove the nearside wheelarch liner and then it's fairly straightforward to establish how to remove it (two plastic screws IIRC).
My brother's E240 did this. It leaked at the joint to the headlight washer just before it went into the unit. We cut the pipe and bunged some "Plumber's Mate" sealer in there. He never used the headlight washers in anger anyway. I think a small tube is around a fiver. Found it on ebay. You can get it at most hardware shops. Here you go. Plumbers Mait Quick Leak Repair Putty 50g by evo stik | eBay