Start with soaking them in a bleach and water solution. 1 gallon of bleach to 5 gallon of water
.
protect the metal races with vasilene.
Let them soak overnite
Take out and rinse
Then scrub them with soft scrub and a green scrb sponge. let sit for 10 minutes
then rinse again
Then if yellowing is still present, use volume 40 peroxide and brush it on the mags and let sit in the hot sun for 4 hours, rinse off and reapply and do other side
You might have to do the peroxide multiple times , i had to do Mark's mags 5 times