I am wondering what do TS wants now?

1. Is TS just want the 2 screws?

2. or the TS wants the seller to bear the cost of repair / refund?
As per the history, the lens is all in good condition till after some time, in this case a month+ then the lens collapsed.

And by the time the lens collapsed, it is under the TS's hand, saying that the damage is caused by the 2 missing screws.
As TS was experienced photographer I believe that there is no issue in installing the lens to the camera, and by the time TS found that it is a little bit loose, TS should find out the caused or inform seller immediately to check.

But this did not happen, leave it aside, TS assumes that the loose might be normal thus did not take any action till the day problem occurs.

And now after sending the lens to Nikon Center, Nikon Center replied that all these caused by the missing screws thus warranty void?

In my 2 cents,

TS should check with Nikon Center what does those 2 screws functions? and how does the 2 missing screws can bring the destruction to the lens?

And TS don't really can blame the seller for anything, even seller gave TS the lens with 2 missing screws, TS should able to determine that once installing it and using it, it is that TS assume that the 'loose' is normal and TS did not bother to check. The lens transferred in good condition and it collapse under TS's care and how can TS claim that is the seller's responsibility?

It is my own opinion and TS, I did not mean to side to anybody, I am just to state out what I think is right.

For other future comments:

1. In the sales thread, TS stated that the photo by lens which means that the photo is not the photo of the lens. It is understandable if you don't understand that simple English but please stop mentioning about the photo.
2. Before everyone keep asking TS to refund because he is at fault, are you sure that the buyer did not intentionally do anything to the lens in the one month's period just because he don't want the lens anymore and need the money. He may denied it butwho knows the truth ? However, silverfire may also be the one that knew the condition of the lens but hiding the fact that he knew about the screws.
3. A reminder to all sellers and buyers, please check your used items to make sure that the items are still in a good condition before you all engaged in any sort of trades. This is to avoid this kind of dispute in the future. We won't know who is actually the one that is correct or wrong in this situation. Furthermore, this matter occurs after a month which made everything much more worse.
4. Stop mentioning the word 'safe trader' and 'demo set'. This both words has nothing to do with this dispute at all. Safe trader doesn't mean that tag is going to be there forever. Demo set is used set. As long as it is usable, I don't see the point of mentioning it. If you want a totally VIRGIN set like TS stated earlier, get a new one then. A used set is always not a VIRGIN set no matter how many people used it. I don't blame you if you don't understand it.

5. Stop arguing and wait for Apis to settle this dispute. At this moment, both sides are possibly wrong. Someone is lying or both of them are telling the truth. Simple as that. So stop arguing and chillax a little.