^Pretty typical for the SLK. My brother's 98 would apparently leak onto his leg if he drove in heavy rain. My 01 never leaked while driving, even in bad storms, but it wasn't uncommon to have a little droplet or two of water on the inside of the side window after a wash (garden hose pressure).
Does the R171 drop the window when you open the door and then bring it up when the door is shut? Our R170's didn't, but many convertibles do (including my XKR, and my dad's early XK8) and in my experience those ones are leak free. Course, the window operating is another potential failure point.....so I'd probably rather live with a drip or two and not have the fancy window thing.