Leaking hydraulic fluid

[Steve Sherman]

A volcano/gusher of fluid coming ou tof the cap is a symptom of a failed
pressure reg valve in the pump.  Check the quattro archives, this is a
common failure mode with these pumps.  High pressure fluid goes back
into the res and forces fluid out the top.

As I recall, it is possible to replace this reg, but it requires pump
disassembly, and the fix does not always work. When this happened to my
5KCS, I just went with a rebuilt pump.

HTH