Yes - this is a common problem with the Mercedes R170 models...SLK230/320 and 32.
I replaced the central locking pump in my SLK230 after months of trying to fix the old one.
Couldn't find one for <$500 though...pretty exxie.
Not sure its much of a problem with the SRT's though.
For the mercs, they eventually lengthened the yellow tubes and turned the unit upside down so water didn't accumulate in the bottom where the circuit board is.
some pics
here.
Not to say it is the problem you have - but it is very common and worth checking. Its not a major job to check.