[old grey steve]

If you've got this fault its likely to be one of several things the main one and I've seen over 100 of these cars would be disintegrating timing chain guides i.e. timing chain guide failure which is as common as muck on these other things perhaps to look at briefly would be oil filter has it been fitted correctly is it old is it sucking in on itself but best bet would be 100% a restriction on the suction pipe assembly that feeds the oil pump and usually its fragmented timing chain guide bits that cause the issue. And trust me you won't necessarily see a timing cam/crank related fault you'd ideally if you smell this sort of issue would need to remove the cam cover to inspect(usually the main support bar for the main chain guide separated drops down and is smashed to pieces by the rotating chain.

Mini's and the later spec N13 engined BMW's have this issue as well as we are doing a 118i at the moment re the valve I'm assuming we are talking about the hydraulic valve that sits on the side of the block usually when removed they are either caked in crap I've seen small particles of timing chain debris within the valve as well plus on at least 4 of these valves when removed they simply fall apart don't. Replacing the valve on its own for what its worth may lose the fault but not solve the problem. Look really carefully to see if there are underlying issues