I have a 1960's vintage French bike that I have had since the late 60's, recently repurposed as an exercise bike on a trainer stand. The bike was used when I got it 45 years ago, and I paid one of the neighborhood kids (a "bike expert") a small sum back then to help rebuild it. There were no other options at the time - I could not afford to take it to a bike shop. Apparently I got what I paid for (not much)!
Have had issues since I started using it again about a month ago with pedals, cranks, and most recently a "creak" in the bottom bracket. When I took the bottom bracket apart, I discovered 19 ball bearings - 15 that are 1/4" and 4 that are 3/16". Apparently he stuck in whatever he could find in his basement. Good thing he didn't own a BB gun, or there would have been some of those in there as well.
I reassembled it with 22 bearings that are 1/4". Amazingly, there was no damage to the bearing cups, and the bike used to ride smoothly back in the day even with the mismatched bearings. I guess the headset is next - maybe I'll find BB's in there. Thank heaven for the internet - I was able to get parts (even cotter pins for the cranks) in a couple of days.