AJ Serie 7 blue chair find  

I've had nothing but good...
I've had nothing but good experiences with Autosol (for cleaning/polishing chrome, brass etc.). It even takes out the black scratches on the enamel of Krenchel's used Krenit bowls.

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my first pick aswell, Autosol. You need some patients, but it works like a dream...

You can use some super fine...
You can use some super fine 0000 grade steel wool with the autosol without scratching the chrome - does it still have the removable grey plastic cover for the leg assembly? The screws look like slotted M8 size but I don't know the length - maybe if you have a sweet Fritz Hansen dealer nearby you could sweet talk them into giving you a set....even if not they'll surely tell you what size you need.
Nice find - my best (only) really was a pair of Carl Jacobs Jason chairs once....I do know a man who pulled an original Isokon Breuer Long Chair out of a skip in Hampstead one rainy night. Also a story used to circulate about a Josef Hoffmann Sitzmachine found in a skip in Amsterdam (but this could be 'urban legend').

no disc
unfortunately, the plastic disc is missing. Not sure if I can get this replaced without taking out a second mortgage.
thanks for the advice

Re-chroming
You migbht want to consider taking it to a re-chromer. That would give the best results. They would even sandblast it first, to save you the bother of trying to clean it up. But hey, what would a well-known journalist know?