I went to look at a 2010 Mazda 5 for sale, with 118,000 miles. During the test drive, I noticed the steering wheel shimmied a little bit when I let go of the wheel. Not noticeable when holding the steering wheel. And pretty minor when I let go. The dealer said it had just been aligned, and showed the alignment report, and that a lot of suspension work was done, but didn't have an explanation for the shimmy.
Front pads & rotors were new. Braking felt fine. I don't think it was sticky pads.

Any thoughts ?

 

Have the wheel balance checked again and also for tire and wheel roundness that can be measured. I would also double check with a different service provider the alignment and also the condition of the steering and suspension parts.
A small amount as you say can be something as simple and overlooked as well out of round by 8-10 thousand of an inche.

 

What's the likelihood it's something more serious ?

 

Sorry, that would be a pure guess from anyone trying to do an internet assessment regarding the vehicles condition without a qualified inspection.

ASE