Mr alao,
I would go with Tar-x, or Tarminator, and some patience. Spray it on, let it soak approx 15 secs or so then see how much comes off with first application, even just a rinse, then apply again in the same manner and lightly dab off with mf towel and by then there should be some significant change in how much of the contaminant is still adhered to the paint surface.
Subsequent applications of tar-x/tarminator/similar may benefit from prolonged dwelling but ultimately I believe it will all come off without more severe methods.
Tar-x/similar may mildly strip some of the protectant you applied but thats better than the current contamination and you can simply reapply another coat of protectant in the affected areas.
Certainly a recent application of any form of sealant would prevent/minimize etching, however thats dependent upon the duration the offending contaminant has been allowed to reside as no sealant can protect forever.
Steve