[RichardJ]

>>the rear lock up before the front is the only time to use the adjustable valve. Mine does not. <<

They must have been talking about using an adjustable proportioning valve added to the rear line.
Yours does not what?

That rubber cover on the cpp combination valve is covering the Metering Valve or sometimes called a Hold-off Valve. The Metering Valve is part of the front brake system. Its job is to prevent the vehicle from uncomfortable nose-dives during light brake application at low speeds.
If your metering valve was leaking, it could have reduced front pressure at all application pressures.

You would need a view of the end of the "Highway Stars LTD" combination valve to make sure the Metering Valve isn't recessed.

Your RED print is annoying, to me it's the same as SHOUTING.