| From what i know, Ducati outsourced the production of rockers in 95-96(?) and because of the financial problems they had at that time, they probably chose a cheap producer.
I opened my 916 a few days ago (4000km since the last service) and found only 1 closing rocker on the admission of the vertical cylinder. The rest are fine. I replace it with a 748 one (2000 model) which seem to be of a higher quality... but who knows?
I'm sure that after market ones are a very good options and if i recall Sigma says they last at least 50k miles!!! | 
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