After months of no MAF on my LS3, the solution was...

[davepl]

...to install a honeycomb in front of the MAF.

I'd been fighting what I thought was an air/vacuum leak. The MAF wasn't seeing all of the air, the car would go lean, both banks of O2 would throw codes for being lean, and eventually a low air mass code for the MAF.

I tried everything, different pipes, different filters, straight pipes with no bends, all to no avail. I was by this time very certain that it wasn't actually related to the MAF. Had tried a different MAF too.

As a last resort I bought a section of 4" pipe with a MAF mount and a honeycomb from eBay, and it works nicely. It's a straight 6" pipe that I can't put a filter on, so some kind of intake tube will need to be constructed, but at least it runs happily now!