I am also experienced in gaseous and hydraulic aircraft systems. The nitrogen I use is 99.9% pure and dry.

It's actually around 78% in the atmosphere but it's the 21% of oxygen that is the problem and if you live in an area like the UK a lot of moisture.

I personally don't want to put 'air' in my £500 shock absorber and I don't think it's fair to advise others to do this either without explaining the advantages & disadvangtages. The only advantage being short term cost.

I wasn't trying to correct you but just sought to clarify for others that air is not what is normally used.
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