Dicky VANOS sensors

My 3 series is going to the BMW hospital on Friday for a new camshaft sensor. Symptoms are difficult warm starting and dog like running below 4000 revs as the valve timing freezes.

Only happens if you get it warm, then leave if for 30-60 minutes before starting it again and then only intermittently. Never happens from cold, clears up once the engine is thoroughly warm again.

However, this is the second time it has happened. Anyone else experienced or heard of this problem, is it endemic?