For a short few years, I owned one of the original 5000 series Deere's (5400) It's "transmission life" was less than 500 hours before it was a problem child. Before 1500 hours, I'd decided to part company with it. Apparently Deere solved the issues with early 5000's. (Or they wouldn't be so popular now)
Under NORMAL use, with average to good maintenance, an experienced operator, and NORMAL luck (Got to factor that in with ANYTHING mechanical) it's not unreasonable to expect 5000 to 7000 hours before any major component issues. Maybe even longer. Not uncommon to see tractors of that nature going 8000 to 10,000 hours without engine or tranny failures. Now, you may have incidental problems with minor parts over the lifespan, but again, that's "normal" for ANYTHING mechanical.