The flashing on a closer look , dosen`t look that clever, the open corners aint going to help.
The silicone sealant on the chimney is simply wrong, combined with at least 3 separate obvious goes at pointing repairs, different colours of mortar, looks like pointing has given previous people,greivous repair despair.
Damp ingress can go from being a minor inconvenience to a major repair scarily quickly, had a 200quid blocked gutter turn into 12grand major roof repair beacuse of wet rot, only took 2 years of everyone thinking somone else was getting it fixed.
If you want a betting game , try damp in ground floor, is it rising damp, interior condensation, water run off from local park, broken Scottish Water supply pipe or alien ectoplasm, alien ectoplasm would be Scottish Water`s preferred explanantion, throw a double six for the correct answer, including if your a surveyor....
Cheers Adam