Canon EF 24-70mm f/2.8L II Lemon? And help w/ Canon Repair Service...

I purchased a new Canon EF 24-70mm f/2.8L II in February 2013 (it upgraded and replaced the original version, which I sold used). In July, after 7 months of normal use, the lens lost its ability to lock focus (on One Shot mode, lens constantly seeks in/out, and is not able to lock on). The lens was sent to Canon Repair where it was repaired under warranty and returned to me.

The lens worked fine until November 2013, when the same issue re-appeared. Again it was sent back to Canon Repair where, again, it was repaired.

The lens worked fine until December 2014, when the same issue re-appeared yet again, resulting in a third trip back to Canon Repair. (I'll point out that for this last service, I called out that this was the 3rd repair, and even asked for the lens to replaced rather than repaired.) The original lens was returned to me, seemingly working fine.

Until this week, where (you know where this is going!)... it lost the ability to focus-lock again.

I should mention I take very good care of my gear (I have 6 other EF lenses in my stable including both primes and zooms). And with each of the above instances, there was no untoward event (i.e., the lens was never dropped, banged, etc.). Literally, one day I'll put the lens on my 5D MkIII body and just like that, it's no longer able to AF properly.

(I'll also point out that in the 3rd service call I returned my camera body to ensure that the body was not at fault - Canon Service inspected it, performed a routine cleaning, and indicated it was working fine.)

I've never had any other issues with a Canon lens so I wanted to ask here: is it worth trying to repair this lens or is it a lost cause? If I should try repair the route, are the better options beyond the Newport New VA Canon repair service? (I've never been able to get beyond a customer service agent and speak with an actual technician about the lens.)

If the lens is a write-off, are there any places where one can sell a non-operable lens (other than EBay)?

This was/is one of my favorite lenses in my kit - it takes excellent photos and is my walk-around selection for trips. So I do want to either repair or replace it. But before thinking about how to shell out another $2K I wanted to ask what folks here thought.

Thanks for any insight or advice y'all might have!