In case anyone's at all interested in this guy, I just came across and killed:
Slippery Sucker -- Leech NM
@ H-8 Qufim Island. No drop.
TOD: 23:04 (11:04 pm) EST tonight (Monday)
Vana'diel time: Lightsday, 14:47, Waning Gibbous moon 62%
He was sitting there as I ran east from the corridor below the lake.
He's ridiculously easy. As 75 RDM/BLM, I hit him with Para II, and then Thunder III to see how strong he was. The Thunder III took somewhere above 600 hp from him; I don't remember exactly how much. I killed him with a couple more nukes and he didn't touch me.
I'd say his level can't be all that much higher than that of the normal leeches in the area. Maybe five to ten levels above? I dunno. I can't tell.
I looked him up afterward, and apparently he drops:
Mystique Earring (Rare)
All races
Latent Effect: CHR +1
Lvl. 40, all jobs
The latent is active while in a party with a BRD.
So yeah, I don't feel like I'm missing out b'cause of not getting the drop ^^