No serious leaks but there is seepage at gaskets ,I don't care much for that,I'm always wiping to keep clean.

 

I'd do It all while it's down. You'll be happy in the end

 

From personal experience I can tell you that you can't see any seeps while you are riding!!!

When you take your rocker boxes apart make sure you check for warpage.
I changed gaskets a few times before I finally checked and when I did I found that the middle rocker box was warped.

 

What wears out in the lifter at 40k?

 

Nothing guarantees your lifters will wear out at 40k but that seems to be the minimum they will last.

 

I was just wondering because a roller follower hydraulic lifter would last several thousands of miles in a V8...

 

Nature of the beast we have. If you are there at 40K ___ replace them

WP

 

Lifters at 40 is normal PM. 50 and you'll be replacing them because something is making noise and at 60 because something let loose.

 

This is not necessarily true.
My bike went 100k on the original lifters.
Well to be honest it was 99k something then the motor got a re-manned for the fun of it.

I'm not saying that it isn't a good idea to replace them at 40k.

 

Couple years ago, I was changing the cam on a reman with 20k on it and found one lifter roller had more slack than the rest, the others were ok, you never know.