Trailer tandem slide repair?

Use a wire wheel along where it's supposed to slide. It's probably just scaled up. You might make it slippery with a bit of 3-in-1 oil, grease will just attract dirt.

 

Pictures of the slides and pins? Do the pins align with the holes?
Some trailers had teflon slides between the two. Yours maybe gone. Sometimes spraying the slide with a water hose helps and wheel chocks.
Maybe try dry slide. Oil products collect dirt and end up worse in the long run.
Be careful sliding on the move. Saw the results of that over the RR tracks. Slider flipped out from under the trailer.

 

I'm sure this is not the approved approach but a squirt of WD or PB in each of the holes on the frame-rail has always worked for me.

 

Water. Wet the slides down good, it has worked for me before.

 

In the first pic it looks like the pins may be dragging on the rail. I’d spray all the guides and pivots for the pins with wd40 or pb blaster and work them in and out a few times. After a day or so go back and spray them with fluid film. Where you see Teflon plate can be sprayed with fluid film. I slide the wheels all the way back and spray the rail,then all the way forward and spray again. Any place you see the rust being knocked off needs to be sprayed.

 

I learned that from the railroad. If it wouldn't slide, they'd soak it with a hose at the shop, and slid like buttah. Only problem, it was a one shot deal, and they'd rust up again. IDK, seems like common sense to me, but soak the rails with a can of "knocker
loose", or wd, or chain lube, ANYTHING, it's not that tough.

 

My old trailer had that problem, worn Teflon plates. A wheel chock, dry lube spray, or Pb blaster, whatever I had. Before loading, sliding it while empty, spraying it good. Otherwise it wouldn’t slide when loaded at all.