Tachometer generator repair

Hi Guys, I have a question re the Tachometer generator at the rear of the engine.
Following under bonnet fire damage (previous ownership ) I found that half of the circular disc with the 2 spade connectors was missing. I bought a new replacement but today when I went to fit there appeared to be a non-conductor type fibre washer which was also broken in half.
As this would no longer be available would an improvised rubber washer surfice. I am thinking in the line of a section of an old cycle tube ?
Thanks in advance.

You could do , or buy a Fibre washer off e-bay !

Hi Ian, thanks for reply.
I do have an assortment box of the washers as shown above but the remains I have of the original washer is extremely thin and shaped to reflect the back of the generator.
Using the above type washer would mean the fixing screws would be too short and I would want to keep everything as original if possible. When you mention Ebay I just remembered that a guy Steve Hunt advertises/sells rebuilt classic Jag, various electric motor and gauges. I will try him. Shall get back to let you all know if I get sorted and how.