I recently returned from a photography adventure in Nepal. It's a very dirty, dusty country. I have a Canon 5D mk3 and a 35mm f1.4L lens. I have been inspecting my camera for damage induced by Nepal and have found that some dust/dirt has gotten into my focus ring. I believe the 35mm is dust sealed, but at the price point this camera is at, I was wondering if this sort of thing requires a professional cleaning by Canon to protect my investment? It has a tiny bit of grinding sound and feel to it, but nothing that seems to be hurting functionality of the focus mechanism at all.
Weather resistant, which is what Canon and other manufacturers claim about their gear, can be a far cry from dust sealed. If you read Roger Cicala's blog you learn very quickly how little he regards the weather sealing claims of the camera makers. Here's the one about the fly inside a "weather sealed" lens. Also note his 1/25/2013 at 6:17 a.m. comment to this blog entry. He has found one camera that he really likes in terms of weather sealing. Roger is the CEO and Chief Technical Guru at lensrentals.com.
If your EF 35mm f/1.4 L has any sort of grinding sound and feel to it when moving the focus ring, then you should probably take it seriously and have an authorized Canon service center clean it.