In my humble opinion, the 757 isn't as robust as the 727, DC8 or DC3 so I don't expect its life as a Freighter to be as lenghty as the aforementioned illustrious aircraft.
Don't get me wrong, I have been involved with the wonderful Boeing 757 aircraft for over 20 years from a Maintenance perspective in both passenger and cargo roles (and indeed I still am).
In the case of the B757 I feel that 'they don't build em like they used to' will probably show itself to be a fact sooner than it did with the 727, DC8 or the DC3. Of course, should the aircraft prove me wrong I would be delighted.
Temps