DAMP IN BATHROOM

We are getting a bit of damp in our bathroom near the ceiling. We had an extension built 4 years ago and I am wondering if there is a connection since we didn't have damp before although we have lived in the house for 13 years. Outside, there is a metal strip going from the roof to ground level between the house and the extension. This is filled with some sort of silicone which has totally dried out and cracked throughout. Water must be able to penetrate the resulting gaps and I am wondering if this could be a possible source of the damp. Any ideas?

Is this damp (brown stain) or mould (black stain)?

The metal strip is a wall tie connector. Yes it should be pointed with mastic, but not normally an entry point for moisture

The stain, which is right in the corner of what was the gable end prior to the extension, is a very pale brown.

The location would suggest water penetration from the roof or eaves, not from the wall