WHO'S GOT THE SCOOP ON RESIDUAL VALVES?

Post #14 is incorrect. When you understand how the braking system works, you will see why.
Drum brakes.
The RSLP valve was not used on a lot of cars, & was deleted on many cars when it was realised it did nothing.
The wheel cyl seals are a tight fit in the wheel cyl bore. If they do not leak when the brakes are applied [ several hundred psi of pressure ], they are not going to leak with zero pressure [ brake not applied ]. When the drum brake is released, the very strong brake shoe return springs push the pistons AND seals back into the wh cyl. Ready for the next brake application. The internal wh cyl spring keeps the seal in place, but in reality, you could probably omit the spring because the friction of the seal against the wh cyl bore would keep it in place. Omitting the RSLP valve certainly does not cause a spongy brake pedal.