[Leica] Separation Question

[charlie at droolassicpark.com (Charlie Meyer)]

I sold an 2,8/90mm Elmarit 1693447 on that 'other' auction site  
recently to someone in the UAE with a Hong Kong domain address.  
First, the package comes back returned to sender, then I resent it,  
including a Leitz UVa filter and the offer to refund shipping as  
compensation for the delayed shipping time.  The buyer receives the  
item and files a PayPal claim stating that there is separation in the  
lens.  I didn't notice any fault when shipped. I had the lens insured  
by the post office. The buyer wants to just return the lens for  
refund when I told him I would be filing a postal insurance claim. He  
stated that the separation was ten years old. I'm no lens expert by  
any stretch, but I am asking if mishandling in shipment could be  
cause the alleged fault.  I'm not trying to shortchange a buyer, but  
if the damage could be caused in shipping, I'd much rather claim on  
the insurance. There is a language difference, which I am not  
complaining about, but I want to make things right, even if the  
listing stated no returns, while not trying to lose my shirt.

Advice appreciated.

Charlie