Signs of oil having run down from the throttle body, very sticky

Liquid oil lying in the folds of the concertina hose between air-filter housing and throttle body

Liquid oil lying at the bottom of the throttle body, and forming a 'bridge' (circled) between the butterfly and the body as the throttle is opened

The breather pipes around the throttle body

Filter (circled) plumbed in to the high-vacuum pipe. With the inlet having a loop of hose below the filter and the pipe coming off the engine, oil is going to gather in that loop before it starts filling the filter. This means suction will have to bubble crankcase air through the oil in the hose, which if the oil gets thick and sticky like it does in the air filter may block the breather. So the hose will need periodic checking and cleaning out, if not replacing.

Just a little oil in the bottom of the filter after 200+ miles, so it is trapping some at least of the oil in the breather. Whether it is trapping all or the majority of it I won't know until I have cleaned the throttle body etc.

The earlier Halfords filter, with no more oil after 1000 miles than 200

The Baldwin filters, supplied in the UK by In-Line Filters. Either the FBW-BF873 or FBW-BF805 appear to be suitable. Many equivalents from other manufacturers are listed for each, but after trying a few to see if there were any other suppliers in the UK but Google only coming up with In-Line Filters I gave up. By phoning round suppliers of the original filters for which these Baldwin filters are equivalent replacements (listed against each Baldwin filter), you may be able to find one more locally. Note this is how the ports are marked, and given Baldwins information (inlet goes to the bottom, outlet is from the top) that is how I connected them. But it seems that the outlet goes to the bottom (not surprisingly) which means it has been sucking oil out again as soon as there was enough to cover the bottom. I've reconnected it the other way round.

The Baldwin filter installed, a little neater than the Halfords, and with a transparent body making any oil easier to see