For one thing, the South African's four-year tenure of the job has been longer than most other senior executives with a foreign passport and an eagerness to enhance a reputation within a big UK agency. For another, he leaves Ogilvy Group UK a better organised and focused business than when he took over, though still far from perfect.
Why have others been less successful? Mainly because foreign imports are too often seen by network bosses as a quick fix. If an agency chief has been able to work his magic in his domestic market, why shouldn't he be able to do the same in a more problematic one? Fine in theory, but, as experience has shown, rarely true in practice.
A confident Matthew Bull, Leih's compatriot, believed he could replicate the success of his Johannesburg agency, Lowe Bull, at Lowe London. In the end, it proved a bridge too far, with Bull unable to stop the rot in Kensington. Then there was James Hall, the ebullient but abrasive chief executive of Saatchi & Saatchi, who returned to his native New Zealand having failed to raise the agency's creative game or improve an awful new-business performance.
And let's not forget the discomfort suffered by Grey London's Californian chief executive, Steve Blamer, during the agency's protracted legal dispute with its erstwhile deputy chairman, Carol Reay. It was a very public row for which his time on the West Coast hadn't prepared him.
If there's a lesson to be learned from all this, it must be that while UK network agencies can profit from the fresh approach a foreign chief executive can bring, the weight of over-expectation can be too much for both parties.