Ram Leak

Can anyone help me. I have an Exchange 5.5 server that a few months ago development a RAM Problem. I have spoke with MCSE Aand there advice was to apply the SP4. Which I did but did not work. What happens is during the week the information store uses about 50 or 60 additional MB’s. Which I reset by stopping and starting the service. Then on Saturday nights for some reason there is a large jump of 600 to 700 MB’s of RAM used by the Information Store. If I don’t reset it will freeze the entire server. If anyone has experience with this please let me know.
Thanks