Ok, it's not a terrible thing that they don't have clustered PKs.
Do they have any clustered indexes in the database at all?
You mentioned that the app has to be restarted to get things to return to normal. Have you investigated the app server for memory leaks as well as performance issues?
Jason...AKA CirqueDeSQLeil
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I have given a name to my pain...MCM SQL Server, MVP
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