Hello; A bearing supplier would not supply defective bearings and expect to stay in business very long. I have been buying bearings for 20 years or more and have never had one fail on me. I have installed them with and without the sheilds and haven't had any issues with them, usually SKF or FAG or NTN bearings occasionally Timken.

Try Steve Webb for your timing shaft, just do a google search for "Steve Webb" and follow the link. If anyone has it, they will.