Yeah, some naphthabrands do have low DMT-solubility. I'm for the moment using a light hydrotreated (what does that even mean?) one that works wonders for the price. I would recommend you get some pure spice and then try a solubility-test (after a evap-test of course) in the naphtha before you buy large quantities or use it in an extraction.
If it seems to dissolve spice it's good but there are other problems. Naphtha (more so than heptane) seems to dissolve everything from none to a hell lot of impurities along with the DMT. When I use naphtha I always wash it with sodium carbonate before freeze precipitation, and this is a must for at least the naphtha I'm using. If I do not do this, I will get quite impure spice. I loved not having to do this with the heptane (and getting great pulls), but it was just so darn expensive.
To-do-list:* Check evaporation, if it leaves no residue then;
* Check solubility of spice, if it dissolves nice amounts of it in room-temperature then;
* Check colour of pull, if really yellow then wash with Na2CO3 + water and;
* Be happy!
I you can get pure heptane, then I would recommend using it for cleaning spice via recrystallization. It works great for that purpose and you need extremely small amounts. 1l will sat for a long while!
There's a clear difference between what I say I do and what I actually do perform.