@laming posted:* Can I use smoke fluid "as is" and not harm the smoke units?
Yes.
@laming posted:* If okay to do so, then what is your favorite smoke fluid for using in PW steam engines with OEM, or like original, smoke units therein?
I think MTH fluid, and Crest fluid, smoke best. Any will work, and it depends on the loco smoke unit performance as well.
@laming posted:EDIT: Forgot to ask... can smoke fluid be had that smells like SP smoke?
You're in luck... JT Megasteam makes that fluid... "Smoke Pellet- (magic smell of model trains of the past with the scent of "the good 'ole days)".