Hi Kathy:

This may sound too easy but get dome Wrights SILVER polish (LIQUID ONLY...very mild). depending on how bad the brass is, let the strike soak for maybe 1 hr and then wash off completely with warm water,...dry completely and you will not believe how nice the brass will look...no discoloration at all and just like new...try it on a common first and you will be sold (Cheap too and you do not have to risk scrubbing the strike!)

PS: My strike's brass tarnishes in airtights too!
Jeff