I have an Actron metal handheld vacuum tester I bought in the 1980's. When it stopped holding vacuum, I took it apart and replaced the O-ring on the Piston and it has worked fine for over 10 years.

If something can be rebuilt or not always depends on the failure and if parts are available and the cost is reasonable. Note and sometimes if you need special tools or procedures.

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84 300D, 82 Volvo 244Gl Diesel