Which SunOS/Solaris version on the master?
Have you tried to monitor memory and cpu usage on the master during the period when issues are seen? (This can be configured by server owner using cron).
The issue could also be with shared memory and not really with physical memory. There are TNs about this (some for media manager processes, but still worth a look).
You will only know the real reason if you can have a look at everything happening on the master during that period.