For 198,
SBS9445S, SBS9640U and SBS9641S have serves 198 since new in 1998
(SBS9445S) and late 2000 (SBS9640U & SBS9641S)
Before being redeployed SBS9372 have been serving 198 since new in
1995 until recently.
For 157,
SBS9055J have been on 157 since 1999. SBS9096R have been on 157
from 1996 until being scrapped early this year.
For 98,
SBS9082E have been on 98 since 1998 when 98 turns FAC. SBS9115U,
also have been deployed on 98 in 1998, have a short stint as 30 in
2000 before being redeployed back to 98 not long after.
For 97,
SBS9105Z, SBS9139B, SBS9158X, SBS9175X have been on 97 since the
late 1990s' and are still serving now.
Also not forgetting those SBS9020J/SBS9022D/SBS9023B/SBS9025X, some
of the SBS930X/SBS931X series VO3X on 30, SBS9073G
to SBS9076Z LO3x from 197, SBS9257T/SBS9258R on 99, SBS9011K
from 143 etc which have been long on these services before
being replaced by new buses.
BTW if I did not remember wrongly those LO2x from 154 (SBS7139P,
SBS7156B etc) as well as 240 (SBS6932Y, SBS6951S etc) seems to have
going through their entire lifespan without getting redeployed.