Uncletits It’s quite a common fitting, it comes in 2 versions, the swivel version which has an O ring in the body and a fixed version which doesn’t.
Lelit chose the swivel version so it’s easy to ensure it lines up exactly with the high pressure pipe. It’s subject to a lot of heat for long periods and removal refit, with associated unavoidable swivel motions probably hastens the demise of both o rings…because there is one in the John Guest style end as well. sometimes they last decade or more, sometimes..not.
https://www.devecchigiuseppesrl.com/e-commerce/welcome/ordini/dettagli.asp?codice-articolo=6R1806&c2=FITTINGS&c3=Push-in&c4=&c5=&Offset=
They are inexpensive and easy to replace.