I would not sweat it. Oxidized lead is still WAY softer than barrel steel. The main problem w/ old rimfire ammo is the priming compound will dry out and fall away from the rim leading to misfires. Age and vibration are the main culprits here. If it has been simply sitting on a shelf it should not be a huge problem. I would not trust my life with it in a defensive situation, but I would not trust my life to a .22 LR anyway.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball