Hopefully, your brass
ports are actually
Bronze.
Sometimes the following work on
Bronze:
Lemmon Juice +
Salt + Flour
or
Baking Soda + Vinegar (Rinse well after)
and always:

Elbo Grease!
OOPS, just about forgot:
After cleaning, I like to put a little "Zip" wax on port lights. Helps protect the sparkle. (Zip is the
cheap car wax, you just add to wash
water - any wax will do, but this is quick & easy)
Lotsa luck, I'm certain they'l sparkle when done!
Gord