Tim's on holiday currently so can't try him, admins don't really check forums much so I don't think a PM here is best course.
I do recall somebody mentioning that you could get in touch with someone in charge of BukkitDev at https://support.curse.com. Not sure if they would be able to get you onto the admins you're looking for.
@AlvinB May I ask you to use SpigotMC BuildTools to older server versions? I need a 1.7.3 craftbukkt server and I would appreciate any help! Thanks!
I'm afraid that's not possible. BuildTools only goes back to 1.8 (when Spigot started making builds using BuildTools). Any other sites you find that offer downloads of CraftBukkit are illegal. But you don't need to get a CraftBukkit 1.7.3 server. Here are some reasons detailing why: https://bukkit.org/threads/why-you-should-update-your-server-and-how-to-revert-sytems-you-do-not-like.445596/
If you really really wanted to, you could potentially use this method to reconstruct an old craftbukkit jar, but I don't think it's worth the effort: https://bukkit.org/threads/help-need-very-early-version-of-craftbukkit.445502/
Depends on how you're vanishing players. If you're using player.hidePlayer(), then you can use player.canSee() to check if the player is hidden.
