I sure this has been answered a billion times. I just gave a wash using W&N oils thinned with Daler - Rowney Turpinoid. Its about a 10:1 ratio of thinner to paint. But when the wash dries, (around a bolt head for example) The paint doesn't dry evenly all the way around it. It's kind of a blotchy stain like the oil didn't dissolve. Is it supposed to look like that? Or am I doing something wrong? Any input would be great.

One reason could be that the thinner is not the proper choice for that paint. As you said, the oil didn't dissolve.

The other thing may be the surface is not even. There should be a gloss coat applied before the washes.