Whilst driving, my 1999 VW Polo has started smoking from steering column?

The garage cannot replicate the smoke or find the cause - after taking the whole thing apart. It is a thin, fast continuous stream of smoke - smells like party poppers. It has happened whilst driving along - mostly whilst it is raining - and the windscreen wipers are on. The mechanics cleaned and sprayed electrical spray - and it happened again - and worse after that! - My car is now redundant at the moment. I have owned it since new - and it is deteriorating in the usual ways - ie. needed new brakes, exhaust, drivers lock etc. recently had new starter motor fitted.