I didn't realise that was a common problem. With the switch on my '69 230, I took the dremel tool and a very small bit and made a bit more of a land where the pin sits so it is more inclined to stay there for a bit.

Another thing that I find helps, is to pull the rubber boot from the column, it was counter productive to keeping the signal on, and it was worse the colder it was.

Hope that helps.

Mark