I replaced mine at about 80K. Then at about 40K later the belt broke 3 teeth and the engine.
After that I replaced it @ 65K on the new engine after that.
I made money on my 81, I owned it for 300K and 20 years.... I loved it and when it came time to sell I discovered money and love can't get you your money back!
I figure I lost at the least $2000 on that TDI, maybe more its been awhile.