Good motors, etc and mechanical function can still generate SMART warnings you should heed. One important function on a HDD that is hidden from the user is automatic fault correction. When it is first Low-Level Formatted, any modern HDD has a large number of extra sectors that are perfectly good - they are just more than are needed for the stated size of the HDD. The unit's circuit board smarts keeps a record of all those. As the HDD is used, every write and read operation is checked by the unit's board for signal quality. If a particular sector is found to give weak signals, it is marked as faulty and replaced with a spare good one, and the data is copied while it is still available. As this goes on, the board keeps track of how many sectors it has had to replace, and how many good spares are left to use. When it gets to a pre-set count, it triggers the SMART alarm. This kind of alarm tells you that MANY sectors have been found faulty and replaced, and there are not a lot of good spares left. The expectation is that this increasing number of faulty sectors will continue until it cannot be corrected and you WILL lose data!
This is one of the most common sources of SMART warnings - excess fault sector count. Do not ignore it. Replace while you can without data loss. A Zero Fill will NOT solve the problem because the sectors are fundamentally poor quality and cannot hold a strong signal. Writing zeros to the sector and then writing data to them will not be any better. Even if you could re-do the Low Level Format (almost impossible without the factory tools), you would not solve the weak sector problem - the basic cause is in poor quality of magnetic coating in that area.
Zero-filling is a technique that MAY help to "solve" a problem of large numbers of "Bad Sectors" according to Windows. But it does NOT fix the "Bad Sectors". What it does is force the HDD to write to and test every sector currently thought (by the HDD's board, not by Windows) to be OK. In this way the board finds ALL of the questionable sectors on it and replaces them from its spare stock. When it is done, there are NO poor-quality sectors in use - they are all tested good by the HDD's board. (As long as the poor sector count is not too high after this, there will be no SMART alarm generated.) THEN when you Partition and Format the HDD in Windows, it only finds good sectors! So Windows thinks the HDD has been cured of all its problems! What has really happened is simply that all the problem sectors have been replaced with good spares - the "Bad Sectors" have NOT been repaired.