Hit the bleeders with some penetrating oil a day or two ahead of time - and yeah some have had problems undoing the bleeders. Make sure to use a 6 point socket for undoing them - DO NOT use an open end wrench.

I had ABS, and when pushing the pistons back in, I did not open the bleeders. Some say that will screw up the ABS, but I never encountered issues at all. Your mileage may differ.

 

I don't open them unless I intend to refresh the fluid. Never had a problem with the ABS.

 

 

 

 

If you have never bled the brakes now would be a good time to Remove&Replace the brake fluid. You should every couple years. Use a MightyVac.

 

I do open the bleeders & use a mity-vac. But shoot the bleeders with Kroil penetrating fluid a few days prior.

Some folks make their own penetrating fluid. 50/50.......... 1/2 part Acetone & 1/2 part ATF fluid.

 

You "should" open the bleeders. Reason being is if you push the fluid back in too fast, you can screw up seals and filters, and if there is crud in the system, it can stir it up and also mess up filters. The system is not serviceable so that means replacement. I always open the bleeders.

 

I've had a lot of success loosening frozen bleeders with a punch and hammer. Place the punch on the area just under the bleeder screw , where the threads would be. Shock that area with a few good raps of the hammer (heavier hammer the better). First try to tighten a little bit, then go the other way to loosen it.
What your trying to do is shock the tapered seat of the bleed screw. Using a quality rust penetrating spray also can help. PB Blaster, Kroil or CRC Knock'er loose are good choices.
I had a nickname "Tilden" because I did so many brake jobs working in repair shops.