If two different drives show the same problems in reading the same discs, my guess is that the problem is in the disc and not the burner.
Do you have problems with burned or pressed discs (or both)?
If these problematic discs are burned media, I suggest to recover all data and burn again on another disc ASAP.
Bear in mind that slim drives are a lot more costly than regular drives, so if you are searching for a cheap solution, an external drive is the best choice.
Maybe you can try to clean optical pickup: slim drives can collect very easily dust.