I have the same issue.
Ever since I replaced my accumulator and revised the ABS modulator the pump runs more often and loses pressure more quickly. It seems to me that it is not the pump itself since I hooked up a pressure gauge to the pump output directly and let it run up to 160bar and left it for a few days without it dropping. When it's all connected up however the oil runs back into reservoir, suggesting to me that whatever "blocks" the pressure inside the modulator is leaking internally causing the excess to run back into the reservoir, it does not seem to be the pump.
Cheers,
-P
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