E91 Mystery Water Leak - NW Recommendations Please

[KatiePlum]

Hullo All,
I have a 2013 320i E91 touring (yes it’s got a pano roof) which has generally been trouble free but now I have a mystery water leak (possibly two). The driver’s seatbelt is damp and cold at full extension after heavy/prolonged rain and there is a small wet patch just behind the gas pedal. The rest of the footwell is dry. The car has been to both my usual mechanic and to the local BMW Indy (Baymow). Everyone thinks it’s the windscreen seal but can’t replicate the fault. So far the following have been checked and ruled out:
Scuttle drains
All the various grommets through the engine bulkhead
All the sunroof drains
Rear tailgate drains
Pillars
Door seals
AC is fine
Does anyone have any recommendations? Baymow suggested a particular windscreen man but that would involve him keeping the car for 3 weeks and taking the dash out. I am not generally a fan of dash removal, sounds like a recipe for squeaks and rattles. Clearly I need to get this sorted out but how? Any advice welcome.

[Court_S]

Have the vapour barriers behind the door cards been checked? These can often fail leading to water ingress.

[KatiePlum]

Yes they’ve been checked too. I had one go in an X3 years ago so they were first on my list. Thanks for responding.

[Glassman]

Bizarre a windscreen man would want the car for three weeks to take the dash out. Surely makes better sense to remove and refit the windscreen to at least eliminate it from the investigation.

De-trim and water test it.

[KatiePlum]

Now that sounds like a sensible plan. Anyone know a decent windscreen place? I’m in Derbyshire but anywhere in Greater Manchester is also fine.