I know what you're using and what speed you're burning at, I can see all that in the log.
Obviously 2.4x isn't working, hence why I said to try 4x. The discs are rated for 8x burning so there's no problem (with overspeeding etc) if you try 4x. The drive may actually do a better job at 4x than it's doing at 2.4x.
Yes, your drive could be the issue... that's why I said to try cleaning it.
If using discs from a new spindle (of the same MKM-003-00 type) and cleaning the drive doesn't help, consider investing in a new drive.