Well, without a new part, you MIGHT be able to repair that one.
It is a flat U channel with 2 O-rings on the outside and some teflon coating on the inside.
It is then sandwiched between 2 plastic flanges.
If it isn't broken yet, then you MAY be able to carefully slide it off the arm.
Replace the O-rings and re-coat the inside with either teflon tape or some paste.
The primary cause for these to wear is that the lower arm often gets neglected and dirt builds up on it.
That dirt then wears a groove into the teflon coating.
In 20+ years I've replaced one on each of my machines.
May seem a bit challenging at first, but it surely isn't all that bad other than the fact you ain't got a whole lotta room in the back to clean shit up properly
so the bolts can be accessed and then reassembled.
The ring will easily come around the lower head, just make sure the arm is fully cleaned and then WD40 so it slides easily.