I just wanted you all to know I had the same problem with my W202. Parking/running lights would flash intermittently all times of the day/night. Ordered a new siren module online. Got tired of waiting for the new unit, so I removed the defective one. I cut around the circumference of the housing where it is welded together. There is a six volt Varta battery connected to the circuit board in the unit. Removed the battery heat shrink, and scrubbed it clean with a stainless brush. Soldered new leads and a connector to the cleaned battery. Screwed the whole thing back together, and sealed it with RTV. I have the new unit, but have not installed it yet as the one I fixed has been working for nine months now.

Just wanted to share as this thread helped me determine the problem originally.