2009 iMac having trouble reading dual layer DVDs

I have two older 21.5" iMacs. One from 2009 and one from 2011. Both running 10.13.6. Both have no issue with CD-ROMs and single layer DVDs. For the 2009 iMac I still have the original System and Applications install DVDs. These are both dual layer, and the only dual layer DVDs I have. I tried using them for the first time in probably 10 years or more. The 2009 iMac refused to mount them. The 2011 iMac sometimes would. I then did some cleaning and polishing with toothpaste (there are visible scratches on both disks), and this helped quite a bit. The 2011 iMac mounts them every time now, and the 2009 iMac does most of the time. It seems to do better after warming up.

I then bought some Verbatim 8x DVD+R DL disks so I could clone these two install DVDs and not have to rely on the sketchy originals. I burned both disks on the 2011 iMac, which can then mount them just fine. However, the 2009 iMac will not mount them. I then burned them using the 2009 iMac and got the same result. Can't be mounted on the 2009 iMac, but no problem with the 2011 iMac.

I know in general these drives are finicky with dual layer disks. I'm wondering if there is something else I should try when burning that might help. Different brand disk? Slower burn speed? Also how about cleaning the drive? I've look at lot at lens cleaning products on amazon, but they seem to be meant for blu-ray players, and I haven't seen any mention of them working for dual layer computer drives. I did use the "credit card with soft cloth" trick to clean the lens. That might have helped a little with mounting the original installer disks, but not the clones.