Melitta Barista T TS - coffee sludge refit rubber

I was about to refit the rubber ring with a u/n shape profile in the pressure chamber.
While taking it out I noticed it was a u/n-shape and which side was up. But after a 30-min cleaning job I finally forgot:(.

Does it go in "n" or "u"?

Can someone have a peek?

I would be very gratefull. It looks like a black O-ring, but when you push or scrab it with your nail it shows a u or n profile. My guess is it goes in "n" open side down to maintain pressure. But I am not sure.

N.B. I saw a maintenace video for a Miele where they advised to replace this similar ring once or twice a year . Depending on your caffeine milage...

I searched the net but can't find instructione online . For sure not on Melitta site. I refuse to contact them because it takes ages to receive a response.

It needs replacement by the way. I suspect the coffee sludge all over the brewinghouse coming from this rubber that starts to leak. Mine even has a gap and is much wider when trying to put back in. Worn.

Ordered a set of rings for this brewinghouse for 13 euro's online. Has 3 o-rings and the u or n shape ring for the pressure house. Should be an annual job anhyway. No mention on this from Melitta.

Cheers.