Black spots on car paint

Brown speckles began appearing all over my white yukon. The dealer said rail
dust, fix with claybar treatment, $300 thank you! The spots started to come
back within 2 weeks. The GM dealer now does a tap dance and with lot of BS.
Who can I take this vehicle too to find out what is really happening to
this paint job. No other cars where I park this car are similarily
afflicted. Thanks

I am guessing you are in the mid-atlantic region. I too have seen the little black spots on my car. My spots looked like little balls of tar and you can scratch the tops of the ball off, but a small spot still remains which is hard to remove? Is this what you are seeing? If it is, you problem is not rail dust, but Artillery Fungus ! Yes I said fungus. In the mid-atlantic region there has been a real problem with this little known fungus which shoots a sticky liquid from it’s insides up to a couple of feet away. The wind can then carry them even further. They grow in rotting wood and mulch. It may not be from your place of business, but rather from your house, or even the gas station you may visit every morning for coffee. (if they have mulch around)

For more information, Dr. Donald D. Davis of Penn State is currently doing research on this annoying fungus

My method of removing the spores is this… I wash the car first, then use bug and tar remover with a 100% cotton towel, as to not scratch the paint. This works well with spores that have not been on the vehicle for a long time. Older spores need to be removed with a clay bar, as your dealer did the first time. You can purchase a clay bar kit in most auto parts stores, under the Mothers brand. A word of caution with the clay bar, keep folding it over, exposing new clay, to prevent built up dirt from scratching your paint. It’s a great way to clean your car, but if not used properly, it becomes like sand paper. I have also had limited success with latex paint remover sold under the M-22 label, but I do not believe this is sold anymore.

To prevent the spores from coming back, you can try to re-mulch the area that you park next to, or replace the mulch with stones as I did at my business.
I have a tip you may want to add. After going through a high pressure wash and super turbo drying the spores stayed. However, if you take a micro fiber towel you don’t need to use any force. You can literally just hold it by the edge and lightly drag and glide it along the surface. This will basically vacuum up the spores. Micro fiber is much better to use over cotton. I don’t know if it’s the design or maybe the electrostatic (especially after wash/dry) or maybe both. My car is black so the actual marks I have to work on. As far as removing the spores this seems to remove most if not all in a minute or two. No liquids. Just a dry cloth/towel and then I just shake it and they fall off.
I tried using detail after with a micro fiber pad and it picked up any remaining ones. I was disappointed at first because I thought they were gone, but now I realize this was step 2 in getting them gone all together.
Microfiber is awesome. Really, look on wikipedia, they show up close why it’s better than cotton. I’m trying to learn about these spore things as much I can so I’ll let you know if I find better solutions.
I was washing my car today and notice many tiny black dots on the rear deck. The dots appear to be smooth against the paint and about a the size of a pencil tip (.5 mm). I tried using a AIO and Maguiars fine polish and the dots will be removed after applying a lot of pressure. i also tried using Rain-X Bug and Tar remover and it took a lot of pressure to get it out. Do any one out there know what this stuff is and how to remove them?