This is a common switch issue- the grease in the switch is dead and contacts worn. Replace the stalk and be done with it.
When doing so, beware the wheel only comes off with the key in the ignition... and make sure you don't break the stalks little plastic return lever when replacing the wheel... then you'll be good to go.
Oh and btw; I think the stalk from any e34 will fit- pehaps even others... check on www.realoem.comNick