Here's my experience. Shortly after I bought my car one of the first things I did was replace the accumulator due to the low accumulator code. After a thorough bleed my ABS light stayed off for about a week or so but then the pedal would get a little mushy and the blinking ABS light would return. Then I tried bleeding again and the same thing, light off for a week then mushy pedal and light back on. I can't tell you how many times I bled my brakes. I put up with this for a few years and then I got PNM's front brake kit so I decided to fix the system. I cleaned the pressure switch myself(and it was sticking, so that was part of the problem), but l decided to have the ABS unit refurbished because I always wondered about internal seals. I sent the whole system off including the accumulator, pump, switch, and master cylinder. I got it back a week later refurbed and fully tested. The internal seals were "swelled" and had to be replaced. The only other thing was some filter had detached itself and probably got in the way of the stroke of the cylinder occasionally, according to the tech. I don't recall feeling anything like this when using the brakes but he said it probably happened. The refurb comes with a year warranty and cost $575USD. It is a lot but I believe this includes a refurb switch and accumulator if yours are bad, since the price is fixed. Unfortunately mine weren't bad so the profit margin was high on my refurb.
Best part is the ABS light is gone and my pedal is rock hard. I haven't had it to the track yet, but I've got time with the year warranty. Actually I haven't even tried to invoke ABS yet., but I am confident in the system with no warning lights. It's crazy to think of how much brake fluid I went through over the years.