The Solder Excursion Diversion - S9-E19
Corrected entry: It's revealed that Sheldon rents out a storage unit that contains literally everything that he has ever owned in his lifetime. How is it that nobody else has ever known about this? He doesn't drive, nor does he take public transportation, and we can assume that he must make regular trips there to store any item that he no longer needs/uses. So he would surely need to be driven there by someone, most likely by Leonard, and he obviously couldn't keep it a secret as to why he needs to go there.
Correction: While Sheldon does not like public transportation, he does take the bus when needed. There are numerous mentions of "bus pants" and "bungee cording himself to the seat" to prove he will take a bus when he has to.
SantaJim