After checking a new, unmounted BR550:
The canti arm rotates on a bushing; it does not pivot on the
post itself. The spring anchor stud is integrated with the
bushing. Once this stud is inserted in the hole adjacent to
the canti boss, the bushing is essentially fixed in place and
will not rotate against the canti post. It would seem that
greasing the post serves to guard against rust/corrosion, not
for protecting against abrasive wear. "Seals" wouldn't do much.