My late 2009 iMac 27" internal HDD was failing (hard errors), and I'd also noticed that the optical drive wasn't able to read CD's any longer.
While replacing the HDD using an OWC kit (to address non-OEM HD FW & temperature sensor incompatibility that could reduce in fast/loud running fans) I opted to replace the Optical drive while I was in there (no sense opening this thing up more than I have to).
Following the OWC installation videos, the process was quite quick and painless for me.
The replacement Optical Drive (and internal HDD) are working well.
If you're only thinking of fixing a failed optical drive, because your original HDD isn't currently having any issues, you might want to consider taking the opportunity to replace both (after taking a good/verified backup of your data to an external drive...). Based on analysis that's been done, HDD failure rates start to ramp up as they reach the 4 year mark, so I feel quite lucky that my 2009 2TB HDD managed to give me 6 years. (http://www.extremetech.com/computing/170748-how-long-do-hard-drives-actually-live-for).
It strikes me that the install process isn't without risk, and so taking proactive steps in an attempt to avoid having to revisit its delicate internals/connectors/cables could be a good investment...