I would say before anything I would probably in this order
1. Try another burned disc of something else, possibly with different blanks since that's the least trouble. I have seen spindles that were like 80% bad discs in the past. Not of verbatim, but it's a thing I've had happen.
2. Ideally, if you have access to one, try another burner.
3. Cleaning the laser is probably never a bad idea if you're confident in doing the work and won't cause damage.
4. I would probably try adjusting the pot if everything before this fails.
5. Replacing would be one of the last things I would try since that costs money and time if it isn't the problem that's just lost time and money, but is definitely an option if everything else fails.
A tear down/pot adjustment guide is here,
can't say how good it is since I only gave it a fast forwarding quick check. I'm sure someone else can chime in with a better guide. When I did my fat I just did it myself without a guide so I'm no expert on good guides. Good luck!