Hi can anyone help, my 1.8 130 silvertop is leakng oil from the rear crank oil seal, replaced it but it still leaks just as bad

Thought must be blowing out due to blocked breather/crank pressure so have cleaned front breather box...dealer says theres a £30 valve in the assembly which sometimes gives trouble, it seems free but may not be working under running conditions, is it worth replacing it anyway? I'm running it on a carb & don't have the output connected to any airbox or manifold at present just vented to atmosphere, is that why it's leaking? Or could it be something else?

I'm sure the seal has been replaced competently & is a Victor Reinz item, oil drips profusely when engine runs, too much to drive car any help much appreciated thanks