I have a 108 that needs the heater levers replaced too...ironically, I've been putting it off because it's been too cold. Anyway, when I do get around to it, I plan to use this guide:
W108/W109 Heater Levers | JaimeKop.com
My first thought with the ticking would be to check for exhaust leaks. Perhaps it could also need a valve adjustment? Maybe someone else can weigh in on that.
For the transmission, assuming the fluid level is ok, check the things mentioned in
this thread. My Euro 350SL shifted hard and adjusting the Bowden cable (as described in post #3) smoothed it out. I didn't have to replace any bushings at the time.