.

it looks like you miss to properly put back some
hose or clamp more than seal issue...

you did not say did you replace just a monovalve or you did
seal replacement... in short,did you see the "inner" parts..?

.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered