Dawn dish detergent on stuck slider pins?

WD40 is a water dispersment.
It's not a good lubricant.
Many people mistakenly use it as a lube... including myself in the past... until I figured it out.

Much better options.
The Dawn will likely work in the short run, but it will eat away at all of your needed lubrication on the pins and rail.
If you use it, make certain to re-lube properly with a good lube after the fact, or you'll likely be sliding metal on metal.

 

Most of those old 40 ft. container chassis had fixed tandems. Try and get legal with those.

 

I ran into this last night. Fancy ### new rental trailer. I went under it to grab the handle to slide the tandems back and it wasn't there but there was all kinds of other crap. I opted to leave them where they were at and just leave a truck hooked to it...