Scenario:

Even after white crystals fall, the tray is dried and a wet looking sticky residue remains. Smells like fuel. How could one clean and separate this from the good product if that happened? Coleman fuel seems to bring problems.

Did you do an evap test to see if solvent evaps clean? If not, you should use another solvent.

It can also be a mixture of solvent that hasnt yet evaporated, DMT, and possible plant oils. You can use some IPA or acetone to redissolve and re-evap it. You can also just keep scraping-rescrapping it and it might solidify/crystallize.

^ I get this often too and assume it's just plant oils accumulating (I re-use my solvent)

But like suggested, what works for me is scraping them from the dish to dry out a little longer on a piece of paper. Any oily residue is either left behind or evapped over the next few hours.