I started replacing the accumulators tonight... when I first got the car the sls fluid was black with oil so I replaced the sls pump and flushed the system from the front, i.e. captured the returning fluid in a separate container until it ran clear. I haven't driven the car much since then, but fluid in the sls container has been staying clean.

However when I cracked the sls valve this evening to bleed off the pressure the fluid came out black and oily, same thing when I removed the lines from the accumulators.

Is this just residual dirty fluid that is difficult to get out with a flush? Should I do anything before bolting the new accumulators on?