Bleeder should have covers to keep out water etc. If you lose them the bleeders will "rust" faster.
Get caps at many auto part stores. Or if you go to a junk yard, get the caps off nearly any car.
Careful use of compressed air to "flush out" the bleeders to remove brake fluid when done then cap the bleeder.
I remove the bleeders, dry if needed for old ones, then coat the threads
w/ Brake Grease
. Not Anti seize or anything else.
Thin coat keep out water in threads.
Don't over tighten w/ or w/o brake grease on threads!
Seal is cone tip to small hole under it. Don't need a lot of torque to seal. I use socket and 1/4 ratchet but only use head end w/ fingers. "Nut Driver" types can over torque them easy too if grasping w/ whole hand and torque down.
Over torque to install often won't break them but will have problems to remove/open again months to years later.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave