What are the sysmptoms of a failing Fuel Pressure Regulator?

My 1989 300SE - M103 motor - has fuel which makes it past the vaccum diaphragm and ends up in the clear plastic vacuum line going from the rear of the FPR to the breather hose (which runs from the VC to the Air Cleaner housing).

Aside from this, the car runs great. I am wondering what the motor will do next as the Fuel Pressure Regulator becomes progressively more damaged.

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Michael Stoic

1979 450SLC
1989 300SE