Most of the Volvo MK4 buses from AMK are operating on St
Michaels' services like service 21, 124 and 131. Hougang used to
control St Michaels' services till 1997 when it was transferred
over to AMK
those
Volvo MK4s could have been perm on St Michaels' services since its
Hougang days 
Service 72, 161 and 168 also have MK4s from AMK too.
Service 162 also have a number of perm Volvo MK4 DM3500s, those
batch of buses began running on the roads in year 2001. It cameoed
on service 25 before in year 2001 before it went to service
162.
As you all have noticed clearly, only those AMK operated bus
services with DD perm buses do have MK4 cameos before, since they
have the rectangular side destos for the DD buses (eg. services 22,
25, 70, 76, 133, 162) 