Hmmm. Burners are so cheap to make and sell these days that they’re not exactly long-lasting (obviously some are more robust than others though), and 2-3 thousand discs is a heck of a lot - and a very good run for a burner
I’ve retired three burners in the last 4 years, and they didn’t get half the use yours has.
Trying some Verbatims would be a good test as most, if not all, burners should burn these very well.
There is another thing I’ll ask for too, if I may - do you have Nero installed on your PC? If so, could you try some burns with that, and if it fails, it should give you the option to save an error log - which you could post here for us to have a look at.