At 160,000 miles, when I replaced my cracked head, my rocker arms were still in good condition.

However, I realize that this may not be the case for everyone.
Good oil and a EGR delete will help extend the life of the rockers (and turbo).

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U.S. Army Retired

In terms of the numbers my sources may not be correct but the breakup listed somewhere in these forums was 15000 card in USA for 05&06 and some 10000 in Canuck nation.