removing blemishes on the roofs of K-Line satin silver aluminum cars

  I've noticed the same issue on the only shiny aluminum K-Line car in my fleet.  It hints that the coating is a thin spray of clear lacquer, with, in your case, an additive to produce the satin finish.  Lacquer, by nature, is somewhat porous and will eventually allow acids and oils to penetrate the surface. 

It's annoying to look at, but unless you're up to disassembling, stripping, polishing and recoating, I'm afraid we're euchred.  It's just as frustrating as those vacuum plated chrome plastic parts that scratch and rub off so easily.

Bruce

I wonder if another coat of lacquer would help or just make a mess.

Just seal it in.  You are faced with ignoring it or stripping and polishing.  If you really like the matte finish and are wealthy, after stripping you could have the aluminum anodized, like Lionel did.

RoyBoy posted:

I wonder if another coat of lacquer would help or just make a mess.

It won't-all that'll do is 'seal' the blemish.

Best way would be strip, polish, reseal