My read of the issue is it's a bit complicated. The TSB for replacing the accumulator was for some original faulty accumulators (early years). However, there are examples of pump failure associated with accumulators that were replaced years prior, or were ones based on later models. For example, the later cylindrical accumulator (for vehicles with traction control) was never recalled (as far as I know), but there are certainly cases of motor failure on those units. The motor appears to wear out - brush failure, wearing down of the stators, and then the dust build up acts as an abrasive and causes more rapid degradation.
In terms of the fix, the accumulator can be replaced in-situ, as it's a simple screw-on/off operation. But at least in my review of more recent posts (2012-newer) it seems that the motor has worn out in the majority of the cases (both toyota and mitsu). The interaction between a dead accumulator and a broken motor isn't clear. Unfortunately you need to pull the entire system to evaluate the motor, which is a +4 hour job and requires a full brake flush. Most people who replace the motor just replace the accumulator while they're in there, because it's relatively cheap, at least compared to the motor.
As far as Ebay, I found that at least the brake accumulator was cheaper there - from a mitsu dealer - than anywhere else. The motor is more tricky, since you can get rebuild/new motor guts from ~$220 or a completely new component for $450. So far, all the reviews/repairs I've read indicated a high quality rebuild has worked great. It's more difficult to get the motor by itself new, it's much easier to find the full assembly which is >$1500.
