The shafts hasnt got to do with the quality of the build but the fact that they are impacted 1500 times a minute just going down the turnpike. The cross bolts only torque to 15ft# and thats suposed to hold but doesnt always and of the 12 you only need one leaking or moving to cause a problem.
Bruce

Get rocked..
 

Saw your post, had similar problems in the past.

For a solution, I would look into TurboKraft's rocker lock set. This kits prevents the rocker's shafts form shifting. Here is a picture from their site:

http://forums.pelicanparts.com/uploa...1270532310.jpg
Click to enlarge

Also, this is why I tend to stick with mostly factory parts! Those aluminum valve covers are a longer surface part that tends to warp when heat cycled. Remove the cover, clean it throughly, stone the surface. Check the flatness of the sealing surface. It is probably tweeked!

Good luck!