Did the 240z's turn signal automatically shut off once you are finished with the turn?(in other words, it had a cog on the mechanism that trips the arm back to the neutral position). I have to manually turn my back to neutral.

 

Yes,..they are supposed to be,self-canceling. perhaps the small plastic parts inside have broken?

 

The grease that lubricates the turn signal mechanism has likely attracted a ton of fuzz, lint, and crap over the years, gumming up the return feature. Remove the plastic clam shell that covers the steering collumn and clean ALL the grease and crud out of the mechanism. Then use some light weight grease to re-lubricate the mechanism. it should work now. re-Install the clam shell.