Oil leak from an E28

My brother's old E28 520 is leaking oil past the front camshaft oil seal following replacement of a blown cylinder head gasket - and head planing. The seal itself was replaced on the head rebuild - and has been done
again. It starts dripping about 10 minutes after a cold start and rapidly becomes a torrent. The engine runs perfectly otherwise.
He's certain the breather system is clear. It didn't do this before the head gasket failure - so is there anything associated that could cause it?
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Crankcase pressure is normal? If you open the EGR system up to air what happens? --scott
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I'm guessing it's a UK car so there's no EGR system, just a pipe from the valve cover to the inlet manifold.
Does the M20 have a spring loaded pressure relief valve on the oil pump? Might be stuck. It'd be worth fitting an oil pressure gauge to see. If I recall correctly correct pressure is about 2 bar.
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Yup.
Could that cause a leak? My brother says there's not excess oil inside the valve cover as viewed through the filler cap.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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