Mine have just recently come back after their second service.
I knew that there was something wrong for quite a while as the bike was understeering badly. When the service was done, it was discovered that the front unit had lost all the oil.
I'm a regular bike cleaner and I had not spotted any leaks. There was some corrosion on the shaft but it was right at the base and well beyond the compression-range of the spring.
Whatever caused the seal failure on mine also buggered the shaft. It had worn the surface so that the seal didn't seal.
All in all, I'd still rather have Ohlins: their performance is far better than stock, then add-in the cost of a replacement unit when the stock item dies compared to repair/service costs.
On this topic, I wonder how many telelever-equipped bikes are being ridden around with useless front shocks? Unless it happens catastrophically, a gradual failure is masked by the steering/suspension design. For quite a while I just thought that it was me or a worn front TKC that made it a struggle to turn where I wanted.