The pictured oxidation shouldn't be a problem ( if the HF drivers VC gap is found to be clear of oxidation ).
- I'd be more concerned about finding lots of oxidation in your Altec 416-8B woofers.
Oxidation adds resistance to the magnetic circuit ( if found where flux lines have to jump across air to metal surfaces ).
More resistance in the magnetic circuit will lower the amount of available flux lines ( within the VC's air-gap ) lowering mid-band efficiency.
That's why ( unseen internal ) oxidation can also wreak havoc to a drivers midband efficiency when oxidation is present at some mated surfaces ( ie; those found in the magnetic circuit > say between the alnico slug magnet and the top-plate or the return pot ).
This internal oxidation problem can only be addressed by someone who can completely strip the driver apart ( for rebuild ) , then re-polish all mated surfaces, recone and regauss . That's a service that's unlikely to be available on your island ( though one never knows ).
I posted your 902-8a ( exposed ) pic because obviously to me your drivers metallic surfaces are starting to oxidize.
- I've just described how that process can start to effect performance ( with no easy remedy ).