Was this the factory fill?
If there are no babbit bearings, and it appears they are using only roller bearings, the lead must have come from a chemistry component added at the factory, most likely Lead(2+) di(2-naphthoate).
Since there appears only to be spur gears involved, ZDDP levels of 700 ppm are sufficient. No need for EP additives.
The analyzed oil appears to about an 80W90.
Yes, this is a factory fill on my Club Cadet ZTR.
Just did a set of ezt’s on a 5 of 2012 rzt50. What came out looked like gear oil to me. The noisy side had a foul odor.
I put couple capfuls of Lucas assembly lube in each, filled with Napa 15w-50 and it’s pretty quiet now.
I pulled them, flipped them, refilled. Vents were clear, no water I could see.