Yeah its easy. An alternator will blow out the diode ring. Easy fix.
Same with starters... the brushes go bad. $3 fix.
Talk about the millionaire next door.... I knew a man that had more money than god and put 6 kids threw college (and bought each of them a brand new car for their 18th birthday) off a small auto electric shop. He'd take the core, soak it in parts cleaner, spray it with silver paint, change the diodes (or brushes if it was a starter) and swap em out all day long for $150 minimum. Pure profit... and he was busy from open until close. The man had his house insulated with $20 bills. Couldn't spend money fast enough.