if you were to sex panaque species using hair on the back part of their body it may lead to a wrong conclusion. Males when ready to spawn or are in good condition will grow the hairy back :lol:. They can also shred the hair within a couple of days.
Best way is to sex them is to look at their heads.
Search the web for L104 and you may come up with some spawning accounts. These plecos have been spawned in aussie a few times in the past year. Articles say that they are easyish to spawn BUT the hard part is to get the females to fill up and also to keep the young alive.