Paul,
The system can be retrofitted with a new or refurbished turbo pump. Do you know if the system has a vacuum interlock valve? You are welcome to email us photos or more detailed serial number information if available.
Since the system has been sitting idle for 4 years, we think a good place to begin is simply by powering the system up and seeing how it performs. Depending upon your budget, replacing the diff pump with a turbo might be a good idea if the electronics are ok and the investment seems worthwhile. Since the system is already having vacuum issues, the source of the insufficient vacuum should first be determined. There could be a leak in the mass analyzer, or insufficiency with either the diffusion or foreline pump. Maybe the GC was also leaking, and the MS system is fine.
Feel free to drop us an email with any photos or additional information regarding the system. Setting up a refurbished GC-MS system is generally a lot of "fun", and can be quite rewarding if you're inherited a real gem. Let us know if we can help.