Larry said it like it is. I have a 1987 300E with 170,800 miles and I'm not evan thinking about replacing the TC.
If it ain't broke don't fix it.
The long life of all engine parts is faithful oil and filter changes. Not twice a year, but frequent whiether your use conventional or syhthetic moter oil. I change every 3500 miles and have for the life of the car.
My engine has never been opened. Not even for valve guides. The oil consumption is 1 quart per 1150-1300 miles depending conditions.
Good luck with your not changing the TC. Save your time and money for Euro Headlights or what ever.
Happy Trails Beep Beep from Houston.
Bye the Bye, throw that Haynes Manual away, it will do nothing but cause you grief.