I currently work on aviation fuel tanks in the UK, the ones I currently work on were built in the 1930-40 period by German Prisoners of war.

The inspection company we are currently using have done several inspections on the tanks over years and told me they have found some SS symbols found on the floor (made in weld)

Today they showed me a Swastika that is still present even after 70 years of use, will grab a pic of it in the next few days, it really suprised me.

No wonder the tanks have lasted so long being German built, if they were british no doubt they would be like a sieve by now lol