Drum replacement on a laser printer

I have an OKI B4100, great little machine. The drum counter tells me it thinks it has reached its end of life and should be replaced. However it is still working OK so, being frugal, I have reset the counter and continued to use it.

Is there any downside to using an "expired" drum?

I hate those type of issues on printers - While the counter tells you that the manufacturer thinks it is time to replace the drum, the bottom line is print quality. You can have it in mind that if the print quality starts to deteriorate that the drum could be at fault and replace it then, but otherwise I can see no reason to replace just because of a counter! What was considered a serviceable part before the counter trips over does not become unserviceable overnight.

just keep going, the image will degrade over time, when it gets to the point of unacceptable, replace.
how long you can push it depends on how good a quality print you want.

you wont damage anything if thats what you are worried about.