Resistors may be OK. I usually only replace them if they are obviously burnt or way way off value. In many circuits it doesn't matter much. Often the stressed ones are the ones that carried a lot of current, like the one between sections of the electrolytics in radios without field coils, then I like to go up one wattage size on that. 20% off could have been what they were when they were almost new. If after a long test run it plays nice and doesn't make sparks and smoke....
