1. That is normal, all lens even high end DSLR will have that issue if you shoot directly into the light

2. Yes

3. 1 Utama

4. No

If it's obvious you can see the dead pixel then it should be covered.

There are various reasons for the flare.
1) Your friend's lens have better coating to reduce the flare (I think this would be the more unlikely than other reasons)
2) What same light source? If it's the sun, the intensity of the glare each hour/day is different. Clouds movement/shade affects as well.
3) A slight variance in angle can also affect/produce/reduce the flare
4) Camera settings/white balance/exposure/focal length/etc is different?

Go for official service centers. Last time i went to those shops offering repair services in digital mall to fix my home button, they unscrupulously swapped my iPhone 4 screen for some cheap quality China made one...