When I had this problem on my 2011 i30, I had the same problem and replaced the damper with a Mitsubishi part that I believe is identical. I thought it made a bit of difference, but after a while it was just as bad. When the clutch was replaced and I could see how worn it was, it was no surprise that I was having problems. Changing the damper might or might not work. I ended up replacing the damper with a solid sump drain plug that had the same thread. No damping (why is it needed?) and definitely eliminates the possibility of a leaky damper being the problem, which it wasn't.
On my 2015 with concentric clutch slave cylinder, I've only had problems when the hose connection to the slave cylinder has come loose, but then you'd end up with a puddle of hydraulic fluid under it.