@Killrob had the same problem in his testdrive of the '55 Verdini.
From the thread: Killrob’s LCV3 Fruinian Supercars - Merano
https://www.youtube.com/watch?v=9eFgL8qpbDY
I don’t think a solution came up, hopefully they investigated.
If they get your car maybe they will find the problem.