That's Just Harry.
You supervise a great team, with one exception. Harry just celebrated his 25th anniversary as an administrator of the university. In honor of the occasion the department signed a card and got together to eat cake. Looking at his recent productivity, though, some people kid privately that Harry has already retired. With increasing misgivings you've given him satisfactory reviews in the past couple of years. Who has the time or stomach to tackle the problem, really? You succumb to the temptation of putting off a realistic evaluation of Harry's performance.
In the meantime, Harry keeps getting older and crankier. The workload keeps increasing and "that's just Harry" is no longer tolerable. The day comes when someone finally calls Harry to account. It may be you, your successor, or someone higher up. Without a documented, accurate history of his performance, the name of the claim is age discrimination.
Like all staff, Harry should have honest and candid evaluations of his performance. Don't single him out for excessive supervision and monitoring, but provide him with realistic verbal and written evaluations. Many managers and supervisors dislike evaluating and coaching poor performers. But, by cutting that particular corner, they expose the institution to liability. The disgruntled staff member may claim that someone of a different race, sex, age, or national origin was treated better. Or, he may claim that the institution breached its own policies in failing to give adequate warnings and evaluations that a problem existed.
Moreover, failure to regularly coach and honestly evaluate Harry takes away his opportunity to improve. If he is not aware of the problem, how can he fix it? It's not fair.
Steel yourself and face the task. If you need additional support, consult your supervisor or human resources.