Nobody is that stupid to share their latest technology with anyone ,allies included. For example, the radar absorbing stealth panels on British F-35's ,will be imported directly from Lockheed Martin based in US and not manufactured under licence in Britain. They won't give the ingredient to the Brits to replicate
I'm not a tanker, but I can for sure tell you that if I am fighting on the same team I want my best ally to have the same technology if not the better technology to wage war than me. I'm just saying, why would you want to ride into battle wearing stainless steel while your best friend rides beside you wearing card board?