what year, model, were do you live?
your fluid may be in need of a flush until clean fluid at all four corners
if you live in a wet area, hydraulic fluid (brake fluid ) attracts/absorbs water over time lowering efficiency and the amount of pressure it can produce .
use a clean turkey baster to remove old fluid from reservoir noting how bad it looks and the sludge that is in the bottom of the reservoir . if it looks bad that may be your problem
time to flush....