Hello Rob,
Check under carpets, boot, anywhere for the on-board swimming pool. Soak it all up with newspapers, towels, sponges, etc.
Why fogging up at 15/1600 hours?
Parked outside, solar heating (sunshine or no sunshine) warms up the car interior and the swimming pool evaporates converting the car into a sauna.
At late afternoon in February UK, the outside temperature drops rapidly and the heavily water laden warm air immediately condenses out on the cold internal surfaces of the windscreen and other glass.
Wipe it off, ten minutes later, more condensation, Seemples!
Walk into a steaming kitchen/bathroom wearing cold spectacles, and you get the idea.
As a work-around, use a dehumidifier to extract all the moisture generated inside the warmed up car, get industrial size water trap bags, or loads of silica gel off ebay, even some cat litters contain silica gel, but eventually gorra plug the water leak wherever that is.
There are logical techniques for finding a leak, one is outlined here, in principal, not for your car, but easily understood and adapted, methinks.
Rover SD1 Forum Snippet #11 - Rover SD1 Bulkhead Water Leaks
it includes this telling process:
# As a general observation, for two people, one armed with a hose and the other with a torch, working as a team; it's possible to play water gently around all the various external possibilities whilst the spotter inside the car searches for water ingress using the torch.
# All glove boxes and local carpets being removed helps the spotter no-end. Remember to start low down with the hose-play, working higher bit-by-bit, to gain maximum effect from the test process.
If leak location remains a mystery, put dry newspapers under carpets etc, and inspect frequently for staining which will pinpoint the approx point of water entry.
