what is the typical life expectancy of a W126 tranny??

[RG5384]

i have a 83 300SD, and i'm wonder what kind of life i can expect out of the tranny. The only reason i'm even the slightest bit worried is the car has about 155k on it, give or take a few miles(odometer broke), and i heard somewhere that the trannies almost always go before 175k! is there anything i can do for this tranny, this late in its life, assuming nothing has ever been done to it, that will help its life? Nothing has gone wrong with the car in a little while so now it's time for to start worrying about prospective problems. I think i always need to have something "broke" so i can fix it Also, when the tranny does go is the car usually worth fixing? thanks again
R