From what I've read on a site devoted to cpap (cpaptalk) some of the older machines are workhorses and some report length of service similar to yours. It would not hurt to plan for the day it does "give up the ghost". Have you had it checked to make sure it is still outputting the proper pressure? Also, many of the newer machines capture treatment data so that you can know if your treatment is effective, and some even have available software so you can monitor it yourself. Many doctors don't retest unless the patient has symptoms of it not being effective. Other doctors like to test periodically to see if the pressure needs have changed. While I do see a sleep doctor at least a couple times a year and have been retested recently because I have multiple sleep disorders, my cpap treatment has been stable for a few years and I just keep an eye on my data at home periodically. If I did not know how my data looked, I may think my cpap treatment isn't working, when it's really my other sleep disorders at issue.
While your machine just may keep on chugging along for a few more years, I think I'd want to begin researching the options and planning to replace it as the primary machine and keep it for a backup. As you are researching, consider if treatment data (not just compliance data), plans to use it for travel, means of battery backup, exhalation relief, and having an option of being auto titrating are important to you. While I love my bells and whistles, I kinda feel that it's like the cars these days - so much more to go wrong than in the old no-frills days.
In the meantime, congratulations on getting such a reliable machine.
It was discovered that I have severe sleep apnea and started out with a C-pap machine and that didn't really work for me, so was retested by another physician and he decided I needed a Bi-pap machine which helped tremendously over the last few years. I've been on this machine for at least 4-5 yrs. and have not been retested. Is there a point in time that I should be retested to make sure that my machine is working for me? Or that my machine is putting out the thrust that it should? I went to one Doctor and after a time of not seeing him, he told me that he was surprised that I was still here! WOW! I decided to change Doctors and after trying 2 different Doctors, the third one was wonderful and have not had any problems with the Doctor or the staff. I'm very pleased.