... and figured I have saved some $400 versus sending it to a shop.
As I have some concerns about my swapped manual tranny, I drained my Royal Purple fill and have a look. The answer: Automotive paint

. So many tiny metal particles suspended in the fluid, and It is so dark even my newly retroed HID can't shine through it. None of my photos of the pan of fluid is good enough to illustrate this, but I see it foam when I pour some of this fluid through a funnel into the pan. OTOH nothing settled to the pan, I don't think my magnet picked up anything significant, plus the car didn't really feel any different afterwards so I don't think the GL-5 RP didn't do anything particularly bad. New fill is one bottle Redline MT-90, the entire bottle of some semi-synthetic gear oil that have been sitting in my garage for years, and just enough of that drained RP to make it overflow.
Next: Fab a bracket for my trunk's CCFL to keep it from falling off all the time.