Turns out my lean codes are now coming from (at least) an apparent leak where the dipstick tube goes into the block, or at least the leaking sound and smoke suggest that.

Perhaps when I replaced the cam cover, the o-ring was disturbed in such a way it is now somehow inadequate? In any case, I fed a plastic tube down the dipstick tube into the sump so I could put the dipstick tube back when i was done, carefully removed the dipstick tube from the block, and I was stuck. I had no room to twist anymore without force to remove the s-shaped dipstick tube.

I couldn't find any instructions on how to get this out. So, I removed the connector to the ABS, lifted the driver side fusebox up and out of the way. My eventual approach was twist counterclockwise and to the left putting the top of the dipstick tube under the fusebox support (note fusebox is out of the way, and the 'guide tube' is still in the sump) with the top roughly parallel to the gap between the fusebox support and the ABS. Then move the top of the dipstick tube (now pointing horizontally towards the left fender) to the left into the gap between the fusebox support and the ABS tubing and 'gently convince' the ABS tubing out off the way to elevate the entire dipstick tube out.

The move under the fusebox support was not immediately obvious to me, so hopefully helpful to others in the future.

 

I remember reading about how difficult it can be to remove/replace the dipstick tube, so thanks for the brief tutorial. I hope it will help on the 4.2 engines as well....

Have you been able to find a source for a new dipstick tube O-ring? If so, where?

Good luck and I hope you have finally found your air leak. Is it leaking oil as well?

Keep us posted....

 

And I thought the big effort was in getting the nut off the bracket.
Thanks Dale and really hope that will solve the problem.

 

1. A seller on ebay, they appear to be widely available (KSH108624).
2. Maybe oil too, but the car has only gone a handful of miles since I replaced the cam cover (maybe 10) since I have not had sufficient time to fully sort this, exclusively to check fuel trims.