Air carrier flight crew reported a hydraulic leak in the wheel well. Aircraft was taken out of service to address hydraulic leak and pooled fluid.

Narrative

During walkaround in ZZZ; I noticed white smoke emanating from the center of the wheel well along the keel beam. During my flight planning; I noticed a previous writeup on Day 0 where smoke was noticed and a hydraulic leak so I was aware of the history and potential presence on the walkaround. From the initial writeup; it further appears that a hydraulic service was performed upon arrival back into the hub station. I believe the aircraft flew 3 more segments until we received it on Day 1 in ZZZ.Initially; ZZZ MX (Maintenance) (Company MX) said that they could see some hydraulic fluid but wanted to check for additional leaks. During inspection; it was determined that there was hydraulic fluid pooled around the shroud around the APU bleed duct inside the keel beam. Tech Ops stated that they could just MEL the APU bleed so that it didn't heat up the pooled hydraulic fluid. While that makes sense to remove that heat source; I had no idea how much fluid was in that area. Of additional concern was the warm temperatures and longer taxi that would cause for warmer brakes. Not knowing all of those variables; and after discussing with the LCP (Line Check Pilot) trainee; concern for leaving this unresolved was shared with Maintenance Control and local Tech Ops as it pertained to putting warmer brakes in the wheel well and the associated heat source around that pooled fluid. This concern was enough to take the aircraft out of service until Tech Ops could remove panels and clean the residual hydraulic fluid. Once clean; Tech Ops ran the APU bleed for approximately 1 hour to ensure that there was no more smoke or any additional source of hydraulic fluid. While all interactions with Tech Ops and Maintenance Control were extremely professional and they reacted in acknowledgment of crew concerns; there is this overarching cultural predisposition to simply defer a system/component that is not the root cause of the observed issue. We were more than comfortable with a MEL'd APU bleed; but that did not solve the issue of the pooled hydraulic fluid in a cavity where it did not belong nor producing an output of smoke. Even more concerning is any potential for a fire in the wheel well or keel beam due to the presence of the standing fluid and other heat sources.It is also concerning that this aircraft operated multiple segments between the initial smoke observation and our flight with this issue. It is entirely possible that it was not observed on some of those flights due to operating in colder temperatures. That said; when the initial leak was found in ZZZ1 it is concerning that there would not be an attempt to clean any leaked fluid at that moment once the leak was presumed to be addressed. Then to only have to add fluid upon arrival after that first writeup; further root cause diagnosis did not seem to have occurred.