How frequent do Shimano bb's go bad
Last fall I suspected something might be wrong but the LBS owner said "those bottom brackets" rarely go bad. Yeah, should have listened to my intuition. Today I was on a 100 mile ride and had to cut it short because of what felt like the bb going bad. A fair amount of "clunking" or grinding feeling coming through the crank arms and pedals. Got it home, cleaned off the bike and slowly turned the cranks on the workstand and something definitely feels right. The bike is a 97 Bianchi Trofeo and 6-7 years ago the bike shop replaced the original Miche bottom bracket with a sealed Shimano unit.
So, how often do they need to be replaced?