Hi ROSSNZWPI, thanks for bringing this up, 100% agree there is a dearth of believable info on Mg treatment options currently available for DIY use. I have 2 sets of wheels needing treatment but given all the contradicting recommendations online I have mostly decided not to address these as DIY projects. Should that plan change, however, I'd go with the PreKote treatment you noted. Everything I've seen online suggests it's a good solution, even though it's remarkably inexpensive (especially compared to possible Henkel/Bondrite options!!), available in small/reasonable quantities, AND apparently free of big environmental concerns.
My understanding of the DOW numbers (1-25 I think?) is that they refer to chemical processes, rather than specific chemicals previously sold by DOW. While maybe some of the chemicals involved may have been proprietary and now NLA (DOW left this business line long back), at least "Dow 7" treatment is a current, viable option for Magnesium conversion coating, and certainly there are others available from industrial coatings specialists. I assume DOW 7 is both hazardous or environmentally unfriendly, and I'm curious what advantages this sort of 'old school' approaches may have over PreKote. Clearly the technical approach differs (i.e., adhesion promoter vs. conversion coating) but it does sound like major players (e.g., USAF) are using PreKote prior to painting some Mg aircraft parts.
Re. the metal valve stems, several vendors must carry them - I recently got a set from Steve Wilkinson.....never thought about the possibility that they could create a corrosion concern. I imagine the securing nut could damage the painted surface of a wheel, but the metal stems were used on many other period cars with Mg wheels (Cromodoras come to mind). Along this same line, I'm not aware of problems associated with the Pantera's steel lug nut seats, which must have been pressed into the wheel at manufacture, so I'm trying not to sweat this potential complication...!