Water stain from rain on panoramic moon roof

[alecela]

Has anyone experienced this? It's a bit of a surprise to me but I have just taken delivery of an 2008 X5 3.0si. There were a fair bit of water stain on the panoramic moonroof which I didn't think would be of any problem.

Little do I know that it's literally impossible to clean. I took it to some windshield/window specialist and they think is due to car being parked and exposed extensive water stain from rain. Certain acidic element of the rain made their way into the glassroof!

Does anyone has any experience in dealing with this? But last option is to replace the bloody moonroof which is a USD$4k job which I really want to avoid...