Temperature light flashing slowly?

[Steve Tinker]

Blonde..
Really, you are over thinking this....
Leaving the car idling for half an hour and then checking fluid levels is not the correct way of doing it. Both oil (9 ltrs) and coolant (22 ltrs) have a sufficiently large volume to expand and register different levels when hot. Plus the oil needs about 20 minutes to drain into the pan to give an accurate level.

To get a base line, check both coolant and oil levels COLD (overnight) just before you set off in the morning. Make a mental note of both readings.
Re-check COLD the next morning or the following morning again if you havn't driven many miles.

The coolant tank & coolant fluid discolour with age, plus the level rises significantly in the resevoir with heat. There's a good chance you can't see the correct level in the resevoir unless you remove the cap and peer in from the top - again inspect when the car has stood overnight.
You have to make a baseline assesment before assuming you have coolant loss or oil leakage....