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You would have to really crank on them to over tighten. Were you using
the correct wrench size, should be 8 mm. Once they're tight they stop
turning. If you actually stripped the threads then they will continue
to turn. Have never heard of those threads leaking. My guess would be
they are under tightened. I'm not saying you can't strip the threads
on a tiny screw like that, but if you're using a combination wrench,
the wrench is small also. With moderate pressure on the end of the
wrench you should feel it tighten up. I always push just a bit more to
ensure they're cinched down completely. You get a feel for tightening
fasteners with experience. These are hollow so they don't take a lot
of torque, but they should be fully tightened into place and should
not leak at all. There should be no brake fluid leakage anywhere.

Do they continue to slowly leak brake fluid or already stopped? Try
wiping the area clean, stepping on the brakes (engine off is fine)
firmly for 1 minute, and checking again  for leaks.

Some of the brake fluid may get past the threads when you pressure
bleed the calipers; or when using a vacuum bleeder air may get sucked
past the threads. What I do is wipe the bleeder thread area clean and
check later.

I use a micro torque wrench (1/4" , -> 250 in-lb) to tighten the
bleeder screw to spec after gently hand tightening it. You can get one
of these for $19 on sale at Harbor Freight.