My 2015 diesel was losing hydraulic fluid, the reservoir is shared by the brakes and clutch. There was also a small wet patch of fluid on the plastic tray under the engine. I found that the flexible hose connection to the clutch slave cylinder was loose, allowing fluid to leak. The clutch uses a concentric slave cylinder which is buried inside the clutch bell housing, it has a plastic arm which pokes out and the hose clips onto it. It is retained by a spring clip which had broken. I replaced the o-ring which seals the connection with one from a set of mixed o-rings bought from a DIY chain for about £2. I used cable-ties to strap the hose onto the clutch pipe, so far it hasn't leaked any more. I bought some spring steel wire with the intention of bending a new retaining clip, but haven't gotten around to it yet considering the cable ties are still doing a fine job. If the slave cylinder is leaking, expect to see fluid seeping out of the joint where the bell-housing attaches to the engine. In my case, that area was bone-dry