I bought a 100 pack of what Log recommended a few years ago and have only gone through a couple. They last a long time even if you remove grip panels for frequent cleanings.The metric size 1.5mm X 3mm works a lot better. Available in Buna, Vitron, or Silicone.
To view, click on metric, 1.5mm, 3mm, and view the material/quanity/price. Or check out the dash sizes and see just how inexpensive they really are.
Same with the metric size- they allow screws to sit flushThe Challis O-rings are thinner, and therefore less durable. But that thinness means that they don't cause the proud screw issue.
The #60 O-rings from Lowes are thicker, and more durable, but your screws won't sit flush. These ones are cheaper, and they can be bought over the counter.
Both work, so you just pick your poison.