Glad you got your issue fixed but I will throw this in here for others that may look this thread up. Lots of PSC reservoirs are notorious for leaking around the cap. I used to think it was part of life but turns out the factory o-ring is too thin. Credit to my buddy Wizzo for figuring this out. Get the next size up o-ring and your cap sealing issues will go away completely. 3mm wide 70mm ID to be exact.
I've also chased a phantom leak that was coming from the front seal of the pump and only when the fluid was hot. Took awhile to figure that one out. Apparently that seal can go out.