I suspect SBS8321Y is replacing SBS6249L for svc 18.
Daily fleet: SBS1940G, SBS6251D, SBS6254X, SBS6233G, SBS6247S,
SBS8321Y.
SBS8321Y cameos on other services occasionally, but it always
return to service 18 the next day. As for SBS6249L, I didn't see it
for quite some time already and SBS8321Y is always doing it's
slot.
6249L on Sv 292 today. 8321Y still on Sv 18 along with 6254X.
Just to update.