Thanks for all the feedback. Hopefully I will respond to everyone.
Temp does not go past 12:00 unless really hot day in summer sitting on really hot highway and then just a little bit.
Does this happen in heating season.... not really but I guess I could answer yes. This happens when the seasons change so in fall I start to use heater and in spring I use it less. I would further clarify this by saying I leave the auto temp set at 21 C and just change the air flow from the vents to be either cool/cold to warm/hot air.
Re the pan. Definitely not from back on engine. The pan I was referring to is right underneath the Rad and there is a air gap between this "drip tray" and engine. The fluid is in the center of this pan, no signs on either side of pan.
Yes I drive this car all year round. No I do not check level, I just wait for light. I will mention again I see this pool under car. I back into garage so under the front end is really noticeable. I see the pool and within a week the light is on.
Just had car in for "Service 2" and the mechanic said they checked and no leaks.
Would a faulty thermostat leak periodically and where would I find this bypass hose?
More info on the Rad service I had a couple of years a go. It was leaking coolant into engine so they replaced gaskets, and hoses and expansion tank. Had a small leak in a small hose, top right of rad and when they replaced it they cracked rad so brand new rad. I was hoping this would be the end of the seasonal leak, it wasn't.
One of the service advisers said if you own a 540i adding coolant was just part of owning this vehicle. I laughed but I beginning to think this is a fact, no a myth.