If you are handy with a soldering iron I would cut the servo lead and extend it to the desired length, more dependable and cheaper than extensions.
If you are using the quad flap setup and your TX has enough channels I would not use a y-harness, put each servo on its own channel.
(sorry I just saw you had a 4 channel TX you have to use the y-harness)
I use an extension from the RX to the wing servo wires.