I have an older Grohe Bridgeport kitchen faucet with a side sprayer. It is different than what's being sold today, as the two valves and the spout are not bridged together, but are separate. The side spray hose started leaking recently and I installed a replacement today. Now, when I turn on the spray, the water continues to flow from both, the rotating spout and the side spray. When I took the body apart, there is a small flap under a spring that is supposed to shut off the water flow to the main spout, but it doesn't. Any ideas?
I am not sure what you mean when you say you "took the body apart", pictures may help.
Residential kitchen faucets with separate hand-held sprayers (as opposed to those where the sprayer is integral to the spout) do not charge the sprayers with system pressure until you trigger the sprayer.
They utilize a special diverter mechanism, usually located in the main valve body. The mechanism is a valve that only actuates and diverts water to the sprayer when the trigger/button on the sprayer is pressed. You need to replace the diverter valve.
The below illustration depicts one type of Grohe faucet that uses a diverter valve, there are very likely others: