Ok... so what is this bit marked in the photo (CRD manual)... The service manual doesn't have any pics which actually show this, since all it really talks about is gearbox removal, not how to service the gearbox itself.
That shot is from underneath, but essentially it's a L-shape plastic tube on the side of the gearbox, half way up. The end of the L faces upwards and appears to have a soft spongy insert (by touch), facing upwards...
I recently got contamination in my gearbox (jumping out of 4th gear unless held there until clutch release when gearbox was hot) and did an oil change.... i'd done a few muddy dips...
When I removed the console boot inside the car, as advised on a different thread here, it didn't look at all dirty in that area, so i'd doubt that was at the top that the contamination happened.
Once I'd changed the oil, the problem gradually alleviated, but didn't stop completely until I did some driving last weekend which actually ran at high revs for some time... then coming back on the freeway, I noticed the problem seems gone!
Perhaps plodding along at 1,500rpm to 2,500rpm (my road driving style LOL) didn't seem to move oil around in the gearbox enough...
All just observations...