Gap in rear boot latch plastic cover (unsure on the actual name of this part)

[calvinised]

The plastic on one side is pulling away slightly and is leaving a gap (see attached). I think it may be the cause of some water being leaked into my boot. Any ideas on how to fix it? The dealer I bought the car from said he could fix the leaking issue in the New Year anyway and it may be some other area that is causing the leak. But it doesn't look great aesthetically.