In one possible implementation, a misalignment-tolerant hydraulic actuator, e.g., for a submersible hydraulic diaphragm insert pump (HDI), has a floating piston that can reciprocate while decoupled from collinearity with a cylinder barrel and a central feed rod that slides through a central axis of the piston. The floating seal can be integrated or provided by a separate insert and provides a pivotable interface between the piston and center rod, allowing these components freedom of motion to avoid elastic deformation, friction, power loss, and early wear when misalignment or transverse forces on an external end of the piston rod are present. Bearing placement can also be selected to eliminate over-constraint.