If the problem is a dinged wiper rack tube, 5/16" fuel line can be cut to length & flared to replace damaged sections between motor & wheel boxes.  Must be no kinks in the rack tubes.

you can buy a new wiper motor for 44 quid now in the uk.. why go to all the bother..  ?? bc

Like so many issues on these cars the smoke was not the problem just the result. As Alex said time to remove the wiper system. I'm having to do what we would call late models. Cars closer to 25 years old rather than BMW. I keep brush kits and park switches so I can address the motor as well. I use the very long oil passage cleaning brushes to clean the tubes. I used wire and rifle cleaning patches also. Steve (CTR) 

Take the whole wiper mech out, dismantle it and clean & grease the cable and wheel boxes.

Something somewhere is bunged up with rust & solid contaminated grease.

So went to turn wipers on and smoke started coming out of the steering column,

Took it apart to find the wiper wire had melted, so brought a new wiper stork thinking it was just the old original wiring was the problem,

put new wipers stork in, wipers started to move very slowly next thing smoke again.

any ideas on this?

I checked the window motor all greased up and seems fine.