Brilliant.
Ingress of water, you could chase this issue for years front to back, these are potential causes if you want to go down the rabbit hole.........
- Heater matrix pipes from the bay into the cabin, check if they are leaking, pretty obvious dampness from around the area under the glove box
- Header seal that runs across the length of the windscreen and down the A pillars
- Blocked A pillar cups
- Poor sealing of windows against the roof seals
- Roof seals on both hard and soft top
- Water ingress inside door card (normally caused by bad weather seal along glass to door
- Sill drains blocked and water backing up (feel behind seat belt tower)
- Sill drain plastic one way flap broken, causes condensation back up from the road
- rain rail on soft top worn or damaged
- rear window seal
- Boot lid seal broken
- Bad rear light seals
- Aerial seal broken
- Condensation around battery where vent tubes are not fitted
- A missing drain grommet (anywhere around the underside of the car)
Probably missed a load, I can't really be bothered to chase condensation issues anymore unless there's actual proper water ingress somewhere as it's just expensive and I don't daily my MX-5s