koamanaz

I just replaced the pads and rotors on my '98 4runner Limited V6 4WD and since the fluid was old and dirty and the old master cylinder was looking pretty tired (yellow and cracked reservoir), I decided to replace it as well. Pads and rotors were stupid easy to replace and the master cylinder was easy as well, but I ran into problems when it came time to bleed the system. I bench bled the master cylinder and bled the lines at all four wheels until I no longer saw bubbles but I still had a mushy pedal that would slowly sink to the floor with continued foot pressure. The calipers looked fine when I changed the pads and I inspected the rear brakes and everything looked to be in good shape. I bled the system two more times with no improvement. Finally I threw in the towel and took my 4runner to a brake shop to have it power bled, figuring there was still air in the system that I was just not getting using the old fashioned, DIY method. When they couldn't get good brake pressure either, they removed the master cylinder and found it was leaking at the rear seal into the brake booster. This brings me to my questions.

1) The master cylinder was a new one, not rebuilt, from Autozone. I can get it replaced no problem but do I now need to be concerned about the brake booster?

2) Since all that time spent bleeding the lines was to cure a problem I didn't have, is it even necessary to power bleed the lines, or if I have a properly functioning master cylinder, will bleeding the lines at home with a helper, the old fashioned way get the job done? The brake shops kept asking if my 4runner had an ABS system. It does, so does this make a power bleed necessary? The only other cars I've owned and worked on myself were all built before 1971 and the invention of ABS, so this is new to me.

Thanks in advance for any advice.