Well, it could be that the "Winstrol" from the UGL's was not Winstrol, or the vehicle was quite different from vegetable oil!
It is very unlikely that Winstrol could dissolve more than rather scarce amounts in vegetable oil, which if I understand correctly you had seen before with another sample, and I was saying that that sample then was unlikely to be Winstrol.
Winstrol has a mp over 230 degrees C. This just doesn't go along with good solubility in vegetable oil. For comparison oxandrolone's mp is almost identical, and many years back I made some oxandrolone in olive oil for myself. The dosing was huge. I don't remember what the volume was -- it was dispensed from a small bottle rather than a tablespoon, so I don't now remember the volume in mL -- but a dose of no more than 30-50 mg must have been in at least 30 mL of oil I would think. So, something like 6 mg/mL at best, maybe less.
Winstrol in vegetable oil would be similar. So I really do think that if you previously saw "Winstrol" powder dissolve decently invegetable oil alone, or vegetable oil with only a modest amount of cosolvents, then that wasn't Winstrol.
Anyway, with your current material, try seeing whether a little bit of it dissolves in 90% isopropyl alcohol. Not that you'll want to use IPA as your vehicle, but if it won't dissolve well into that (say, 20 mg/mL) then it isn't Winstrol.
Oh and btw, that's another illustration: with the solubility in pure alcohol being only about 24 mg/mL, the solubility would have to be much lower in vegetable oil, or vegetable oil with only fractional amounts of cosolvents.