Yes, clean the airlock, sanitize and return. This happens with a lot of brews (but it is hit or miss). I would suggest you use a blow off tube instead of an airlock during the first week of fermentation. You basically use a clean sanitized piece of tubing from your fermenter "hole" and stick the other end into a container of sanitizer. This will allow the gunk to be contained. This can be done with buckets or carboys. Mine looks like this.... It's just a much bigger version of an airlock.