Perhaps this was asked before but I was wondering what is the average longevity of a CD laser. I understand, if it burns out ,
it can be replaced depending on the brand. 
Indeed, this has already been discussed before.
I agree with some of the advice given here but completely disagree with the rest. Keep in mind that when people refer to 'a laser', they're actually referring to a laser pickup assembly, sometimes also called 'a traverse'. It can and does fail with time, for various reasons. The servo IC can get damaged, the motors that move the diode across the rail or the focusing motor can fail and yes, the diode itself can fail due to changes in the chemistry of the inner gas. The 'assembly' is a vital part of the mechanism and as such it is a relatively delicate affair that is best replaced as a whole. Replacing indivitual components would be tricky, not only because the components are tiny, but because they require precise electrical tuning to work optimally. These specs are usually not provided in service manuals as the assembly is typically sold as a package.
Some assemblies are more robust than others. Just because a Sony KSS-213 is used in a cheap Cambridge Audio player (which I still consider proper HI-FI) and a very expensive Accuphase player does not mean you bought an expensive player with a cheap mechanism. The designation is the same but the mech in the expensive machine will be tested, retested and tested again before it's even taken off the assembly line. Special amplifiers will be used to provide stable light emission by the diode, the motors will be Japanese, not Chinese, and the servo will be highly optimized, not generic. Still, in all fairness, only very nice Japanese players receive such treatment.
I assume you're referring to the Bryston BCD-3 player here. Be aware that Bryston, like mostly every other boutique high-end make, does not make their own mechanism. That, however, does not mean they simply buy the mech from someone, install it and call it a day. They may have done special modifications to the drive, either themselves or by the drive manufacturer, to adapt the drive to the partnering electronic and mechanical design of the product. It is very likely that only Bryston would be able to sell you a replacement drive and you would not be able to buy it from the original manufacturer. Even if the drive looks the same and haa the same designation, all it takes is a small modification in the firmware for it not to work properly. Don't quote me on this, but I seem to remember reading something about how this was precisely the problem with the original BCD-1 drive - made by Philips, except that the generic Philips drives did not work even though they should have.
Seems like I have something against Bryston players. Not at all - they're wonderful players. As such, I think it's worth taking a bit of time to investigate how to prolong their life as much as possible.
Hope this helps. Cheers - Antun
