size of rubber donut under horn button 54 KM

[retroguy]

Anyone know what the thickness of the rubber insulating donut under the horn button should be?  My horn would blow constantly, so I added a 1/16 spacer on top of the donut.  Original thickness was 7/16-1/2".  Problem seems to be solved--at least until I take it out for another test run.

[kfnut]

Replacement rubber donuts are sold by the manufacturing fund .

[retroguy]

Thank you