If the sliding door fits flush to the body all round then you need to renew or pack out the existing rubber seals.
If not flush fitting then adjust the door lock latch (two torx bolts, mark existing in case you need to restore, loosen bolts just enough so you can move the latch plate) If, as seems quite often the top of the door still protrudes then measure by how much, remove the top roller arm and bend in towards the mount by the same measurement (great care not to fracture the arm...they are normally good for 25mm)
There is also adjustment for the locating peg below the roller arm, can sometimes be good idea to get a pair of molegrips on this to make sure it enters the slot cleanly. If there is no plastic guide in the slot buy one and fit (they push through-you might get the old one(s) by removing the electric button strikers at bottom to access the body cavity where the fall.