Found a nice looking 16-35L Mk1 locally for an incredible price and scooped it up.
It seemed to be front focusing a bit on my 40D, but within a week I switched to a 50D and was able to take care of that with the AF micro-adjust. Last week, however, It suddenly stopped wanting to lock focus beyond about 28-30mm. Wide, I can get it to focus and lock...zoomed in it just hunts for focus really bad. Often, it will seem to "bracket" the correct focus but never lock and then after a couple seconds, will start running the full focus "length" in and out. My other lenses work just fine on the body. I no longer have the 40D and I don't have access to another Canon body right now, but i'm feeling it's a lens issue, not a body issue. I've pretty much decided to send it into Canon (the price I paid for it still makes it an amazingly good deal) but I thought I would see if there are any ideas out there that I should try first.
I have done my best to ensure the lens and camera body is clean, and that the contacts are in good shape...however I was a bit limited in cleaning "supplies". (Blower, brush, pencil eraser for contacts)
Interestingly, when I cleared all the custom lens focus settings and disabled that feature in the CF, I briefly got get a lock if I "helped" the focus or started almost right on focus before shutter press...However, that success was short lived so it may have been an anomaly rather than a possible link.
Searching the internet, I have not been able to find any other similar problems/solutions...I guess in some ways that's a good thing...
Any ideas you have would be appreciated.
Thanks!

Greg, make sure your lens does not have sticky aperture - change aperture setting and use dof button to verify it.

I appreciate the idea...Just checked it and aperture works just fine, no stickiness at all.

I suspect that is why it was for sale. The lens may have been dropped and have internal damage.

EBH

Yes, that is a possibility. I would expect more evidence and other issues, but if I end up having to send it in, then we'll find out.

Sent my lens in to Canon today. When I get it back, I'll report the results.

Greg -- Looking forward to hearing what you find out. Hopefully all will be well at low cost.

Canon reports $179 to fix...No details yet as to what the problem was...
A local service guy said something about a feedback issue/loop or something possibly. He didn't seem too alarmed about it but said Canon service would be best/cheapest method to fix.
Will report when I know more.

Got my lens back already!!! I had been told to expect Canon to take their time fixing my lens...3 weeks or more...well, either they are better than some think or I got lucky! 7 days, including shipping and a weekend to get my lens taken care of. Focuses fast now...
For those few out there curious to know what was fixed...here is the list:
Main pcb ass'y, focusing ass'y, zooming brush, zoom fpc was replaced.