The UK CAA issued airworthiness communication number 2009/05 entitled
Maintenance of Instrument Vacuum System Components.
This deals with the subject in detail and it begins by citing the loss of a Piper Arrow in 2007 ( a fatal accident) due to a failed vac pump (12 years old 994 hours in service).
If you go to the CAA website airworthiness section and search for
AIRCOM 2009/05
you can read it in detail.