No idea, but if you can lift the large hose in the top, and it lifts easily with a brass tube attached to it, then the push-fit tube clamp that is supposed to hold it in place has failed and allowed oil fumes to coat the outside and mix with dirt. Inside should just be oil that gets recovered from crankcase fumes and drains to the sump.
The clamp is part of the vacuum oil recovery unit body, and is supposed to comprise a ring that you lift to release the brass tube, as found on push-fit plumbing. If it's missing or damaged (common) it's not available separately, so either you replace the entire unit, or devise some sort of DIY seal, or put up with it.
Mine is missing entirely and is on the list of things I'll get around to at some point. Having cleaned it up a couple of months ago (brake cleaner and a cloth) it's stayed fairly clean and is going to take a year or so to get messy again. I think just shimming the tube with some recycled beer-can, with or without some silicone sealant, would do the trick. Otherwise I keep forgetting to look at actual push-fit plumbing connectors in B&Q to see whether I might be able to cannibalise one. The brass tube is about 22mm OD (though I also keep forgetting to measure it) so it may be possible.
BTW the separator is awkward to remove from the back of the engine. There are 3 bolts securing the frame. It's possible to see one and a bit.