I got into an accident in the rain and later found out my brake line was leaking, so I replaced it all the way. I bled the brakes and still found that the pedal was spongy so I replaced the master cylinder. The MC was seized to the booster, so I replaced the booster.
Still spongy. I then found out that another seal in the NEW master cylinder was faulty, so I replaced it again and bled all the brakes once more in correct order. Still spongy, I can not seem to figure out the problem and I would like some tips.
Please help!! I've been at this for weeks now trying to understand. Thank you!

Are you bleeding the Master Cylinder before installing it? If so, how are you doing it?

Bench bled on my vise with a nut driver multiple times, tapped the cylinder and installed. Brake pedal doesn't go all the way down to the floor so I don't believe its the master cylinder.

It took me forever to bleed my new master cylinder. I kept seeing bubbles floating out of the reservoir. Whatever the amount of pumps was suggested, I ended up doing twice that. I think you almost want to tilt the cylinder a little bit for some of the process to get the air to move around and come out. Other than that, bleed your lines again and check for leaks. Good luck.

It is really hard to bleed the brakes on these things. I had a hell of a time after doing a rear disc swap and they were spongy as hell after about 4 attempts. Finally took it to Brakes Plus and spent the 50 bucks and they were able to get them bled great. They have a machine that does a much better job than we can in our driveway. Not saying it can't be done, but my time was much more valuable.

On the subject of bleeding brakes:
- Bench bleed the master before installing (check)
- Have a helper pump the brake pedal a few times then hold. Crack the line(s) one at a time at the master cylinder to let any trapped air at the line(s) out at that exact spot.
- Gravity bleed at the right rear, then left rear, right front, then left front.
- Sometimes, a reverse (pressure bleed) is necessary.

As far as spongy pedal goes:
- Check the rear wheel cylinders to make sure they aren't blowing brake fluid all over your shoes.
- Check your hoses to make sure they aren't turning into balloons when the brakes are pushed.
- Check your calipers to make sure the slides aren't jammed up. I've seen that happen a few times.

Had a helper bleed the front brakes, okay.
Gravity bled the rear in correct order as well.
Brand new wheel cylinders, now when I push the brake pedal, the sound of air is coming out so I am assuming that the brake booster is faulty, even though I had replaced it with an SKP manufactured one.

check those new wheel cylinders to be sure the bleeder is above the brake line. if not, they are on the wrong sides.

..

How did you go with this?
I know its a year old but OP was active last month.

Having had a spongy brakepedal and air hissing for a long time as I can remember I'll need to revise that since my front wheels are now pretty much locking up after a 10 min drive...(might just start e new thread but thought to ask how this went first)

Some years ago I put in a new MC in and bled with over 1 liter of fluid without any change.