Dont know anythin about the differences in cap however, the way i flush power steering fluid is to pull the return hose off the reservoir (will run up from the rack). Put the end of the return hose into a container, top up the reservoir and leave the cap off. Get someone to start the engine, the fluid will start pumping out of the return hose, at the same time start adding new power steerind fluid into the reservoir. Turn off the engine when clear/uncontaminated fluid flows from the return hose into the container (dont let the level drop too low in the reservoir as it will allow air into the system). Reconnect the return hose top up the level and check for leaks.