I never knew there were 3rd party Platinum converters! Do these work? I'll order some.
Are there 3rd party Sailor or Pilot or Parker converters?
The only type of converter I know you can get for cheap (and I did) are standard international, which worked in my Waterman but won't get into any Pelikan. I despise how Pelikan made their nipple and the trouble with converters!!
To the OP, for any highly staining ink like BSB I'd refill cartridges. It's quick and easy, even though it sounds like a right kerfuffle. I think you can refill Platinum carts even via eyedropper, the opening is quite wide, but I always have used a syringe. Imo Platinum, Sailor & Pilot carts are the very best around, I have yet to wear one out on me and I don't even strictly remember which one I used how often, but they last and last..
Or buy these cheapo 3rd party converters and tell us (me!) how they are! I'll for sure order some too, gobsmacked they even exist and the price is quite good. Irresistible, really.
Btw, I have once used the Platinum adaptor for international carts and had no trouble getting it out, all it takes is a good pair of tweezers and a bit of muscle power and it gets out. The side where I pulled it out was a bit mangled (I didn't grip it well enough), but it has no effect on performance, just don't grab the nipple, but the side.