Glad you got it sorted. Thats a fine air pistol.

In the UK if its a surface bloom and not pitted yet - try a gentle dab with Duraglit. Its lint or wadding with some type of solvent in a tin. Its quite gentle and will remove surface rusting with no damage to the blue. Seems to neutralise the rust too. Think Brasso did a similar product.

In the US there is probably a jewellery cleaner that will do a similar job.

Climate sure is kind on airguns in parts of the US. There are some beautiful condition Bsa underlevers there - they don't seem to pit. They just go a smooth even blue brown patina. Even the etching survives !