I'm not sure whether it would be good to bring Hamer back or not and I'm happy to trust FL's judgement on that. That said I just don't see Sheff U selling him back to us.
Nevertheless, while it seems as if Hamer likes a beer and the odd kebab, there is nothing to suggest he does not train to the highest standards. He is a box to box dynamic player, and you cannot be that if you don't train properly. Some players metabolisms allow them more leeway than others, and perhaps Hamer is one of those able to push it more than others. For example to the extremes compare and contrast Bryan Robson and Darren Anderton! Closer to home Sheaf was one of those players that would not play at the whiff of a niggling injury whereas I always felt Hamer would play through a minor injury. There is little doubt which player is more inspirational to team mates.
I think you are being unfair to Sheaf. Some players suddenly become injury prone at times during their career and I believe Sheaf falls into that category. Gareth Bale is a classic example of a player where his injury problems were predicted early in his career, due to an unusual running style.
It is a shame, because a fully fit Sheaf was a great player, which is why Prem teams were looking at him. Think we sold Sheaf because of his propensity for sustaining injuries, not because he was somehow refusing to play with niggles.
In the modern game, there are well qualified medical professionals that make decisions based on player wellbeing and the long-term benefit to the team. Gone are the days of give him a cortisone injection and roll him out on the pitch. Players often play at less than 100% fitness, but not to the detriment of their health.