Hi ! I think the problem is a cracked Thermostat Housing (covered under warranty). I had the exact same symptoms on my '06 and the SA said this is very common since they're made of plastic. Had it replaced about six months ago and no problems (or drips ) since.

Papa Dude

 

First I think I would lower the level as water dose expand as it heats. I would get it back down to the max level and than check it from time to time to see if the level stays constant.

 

I hate to say it but I have a problem, still. I got the thermostat replaced and it looked fine, however a few days later when I went to wash under the bonnet i was some what shocked. As I look at the engine on the left hand side were white dots, what appears to be dried up radiator fluid... not positive. I check the radiator cap on the right side of the engine and it was very tight, however there was signs that the fluid had come out and dripped over everything around the cap. Honestly I can't be bothered looking around for the issue, and the reservoir has already drained in 4 days. Its booked in for a fix tomorrow, hopefully it all goes right.

 

I am sorry to hear you are still having problems. It sounds a lot like what I went through myself ( as I stated above). First the thermostat froze closed. Replaced that thinking all would be ok. Not so - still lousing fluid. Next I replaced the overflow cap. Still lousing fluid. Lastly I took the overflow tank off and low and behold I noticed a slight gap on the rear seam of the overflow tank. Replaced the tank, which came with a new cap, and all has been fine ever sense. You will let me know if that is what your dealer finds. You are fortunate that you are still under warranty.

 

I just lowered the level to the max line. There was 1 L extra in there!

I'll keep an eye on it to see if it continues to leak. If it does, I'll get the expansion tank ($28-$30) and try to install it myself.

 

I got back from the dealer after waiting for 3 hours Got some chips fixed, however I was a little annoyed that Daisy was just sitting in the back parking lot for a good 45 or more minutes doing nothing. When I get her back I was told there was nothing wrong... yeah BS. It was pressure tested, but its not normal for the reservoir tank to drain empty in 4 days after it got fixed. Ill wait and see, hopefully it cured itself...

 

I've been pushing my luck, my coolant tank is weeping at the seams. (03S) I know these are prone to split, on earlier years, and I am going to replace it. My question is, should I replace it ASAP, or can I push my luck a little longer. Say after 300 mile MINI5280 club ride? Confliting schedule, unable to get to get a new tank from the dealer before this event, Sat. 1-31-09.

 

Mine weeped from the seam for 1,000s of miles before I had it replaced (my closest dealer is a long ways away so I put it off until I had other problems). If it has been weeping for awhile and has not been getting any worse I would not worry too much.

 

It's gettin' worse. I'm going to chicken out and play it safe. Going to give Schomp Mini a call after this post and see if they have one.