Brake fluid question

So i have some new brake fluid ive seen a couple people say you can just empty the master and refill it as a fluid "change" without flushing it via bleeds. So is it ok to only replace master cylinder fluid and let it mix with the old fluid? I ask because EVERY car ive had EVERY time i try to bleed a brake the freaking bleeder valves brake off never been able to get ONE to not snap off. then it turns into a huge project of either new calipers or drilling out the old valve and replacing it. Also im pretty sure it is fine but is it ok to mix synthetic DOT3 with "non"synthetic DOT3 i think its fine since its DOT3 all around but want to make sure before my brakes would fail from something.

OK well i dripped a couple drops of brake fluid on my fender. i wiped it up immediately, then got a cloth with water and wiped it then got a cloth with dawn and wiped it, then water then dawn then water then dawn. than i hosed it down for about 5 minutes with the garden hose. you guys think the paint will be ok in that area?

So i have some new break fluid ive seen a couple people say you can just empty the master and refill it as a fluid "change" without flushing it via bleeds. So is it ok to only replace master cylinder fluid and let it mix with the old fluid? I ask because EVERY car ive had EVERY time i try to bleed a brake the freaking bleeder valves brake off never been able to get ONE to not snap off. then it turns into a huge project of either new calipers or drilling out the old valve and replacing it. Also im pretty sure it is fine but is it ok to mix synthetic DOT3 with "non"synthetic DOT3 i think its fine since its DOT3 all around but want to make sure before my brakes would fail from something.
I would not mix synthetic with regular!

If you want to replace fluid - replace it.

Try to spray some penetrating oil on the bleeder screws. If the screw is stuck, try to work it back and forth.

Good luck,

Sam

OK well i dripped a couple drops of brake fluid on my fender. i wiped it up immediately, then got a cloth with water and wiped it then got a cloth with dawn and wiped it, then water then dawn then water then dawn. than i hosed it down for about 5 minutes with the garden hose. you guys think the paint will be ok in that area?
I do not think your paint will suffer from the brake fluid. ...it may be damaged by the Dawn (may be). Just leave it alone.

I am using brake fluid for removing regular paint and I should tell you that it takes a while for brake fluid to soften the paint. And this is just a regular latex with no clear coat.

You should be fine.

Sam

Spray the screws with PB Blaster or other rust loosening penetrant then tap the end of the screw with a hammer before trying to loosen it. You're better off trying to get all the old fluid out since if there is rust in the pistons it's not any good anyways. Plus they're usually pretty cheap to replace.

If you have to mix synthetic and nonsynthetic you can but you can't mix DOT3, DOT4, DOT5, etc. You are better off having a single type of fluid as its behavior is predictable than as a mixture.