With top down driving the laser does get dirty quicker than a home unit or in a hard top, when I had the OEM HU I had cleaned it a few times a year and resolved the issues.
Here is a link to what I used but if you search I am sure you can find similar or better.
Amazon.com: Discwasher Rd1142 Cd/dvd Laser Lens Cleaners [2-brush; Wet]: Everything Else
