The Ford Dorset and Dover series 4 and 6 cylinder engines normally vent from the rocker cover. Is this breather you have original or has someone added it at some point. I had the Dover 4.2 litre 4 cyl engine and yes at full speed with the turbo singing it does have a bit of blow bye. So yes it needs an engine breather, but the 3/4" pipe off the rocker cover vented outside the engine compartment was fine. You are risking blowing out oil
by having the breather in the sump. At least the oil
drips down the block from the rockers rather than out the breather.
There was a kit to provide an oil sump drain with the Dover series, but it was so slow when changing the oil I took it off and stuck a sump plug
in it. Used a vacumn pump to remove the oil when it needed changing.