May be this will help you a Bit! or same is the case with your City i-vtec
I had this Problem with my City i-DSI Rear Light,
In the Main Circle Light, I saw their were some Dead Flies, Detached the Part of Carpet that is on top of Light, What i found that in the Light their is another open part other than the Core in which the Light is Attached.
1.Took Vacuum Cleaner, Detached the Bulb, Through the hole, Took out all the Flies Using Vacuum Pipe.
2.Through the Open Part Inserted a Damp Thin Cloth for Cleaning the Other Dust, Dried it through another Dry thin cloth.
3.Covered the open Part of the Light with Tape.
After that Day My City's Light is Clean & Clear, May Be This City's Light also has some Open Part Inside, By Default. Check it.