I had 5 version 1 lenses, none were really good. The AF issue is likely due to some 5 cent internal plastic guides that crack, or break. You can replace them yourself. Thher are also internal lens adjustments that seem to need tweaking over the life of the lens which goes out of adjustment due to bumps.
The 24-70mm f/4 is not likely going to be a improvement, its about the same as the 24-105mmL.
I'd recommend having your lens tuned up. It might cost you $300, but you should see a big improvement. The one weak area is the curvature of field, at wide apertures, the edges will be oof, or if you focus at the edges, the center will be soft. This is a lens design issue and can't be fixed. Its only apparent to those who obsess over IQ.
I have both the 24-70/4 and the 24-105 and the former is significantly better across the range and much better in the corners. Early copies that were reviewed do not seem to have been assembled that accurately; it has an unusually large amount of adjustable elements apparently.
I have both as well.
However, I have different impressions. Both lenses have their own strengths and weaknesses and I have come to the opinion that one can't truly replace the other.
The 24-70 has better:
Performance at 24mm, particularly in corners
Distortion control at 24mm
T-stop advantage (slight increase in exposure despite both being f4)
The 24-105 has better:
Performance in the 50mm range (significantly better, too)
Performance at/near MFD
At 70mm both seem to be about the same TBH.
Now, you may mention that I didn't bring up the close focusing ability of the 24-70 as an advantage over the 24-105. Why? I find it to be incredibly soft, plus one has to get so close that the lens blocks light. Not that useful in my opinion, but nonetheless it may find some use when I can't be bothered pulling the 100 macro out.