new laser/assembly for Cary 303/300 cdp

I had a CDP 300 with the same problem. Cary was using Pioneer transports and the glue used to hold the laser cover would fail. Mine came completely off and would not read any cd's. Cary was able to re glue mine and service the player for around $150.

The SL-710A drive can be found in some very inexpensive dvd players. My Resolution Audio Opus 21 also uses that drive. When mine was having trouble I did a lot of research trying to find the drive at a reasonable price. My research also showed that drive to be a fairly problematic drive.
Ended up buying what was claimed to be an almost new dvd player on ebay that had that drive in it. Sure enough for about $30 I had a like new transport ready for install from ebay.
Unfortunately, I threw the case away or I'd take a look and get you the model number. Google is your friend if you decide on that route.
As for cleaning the lens, I'd take a qtip with a light alcohol dip and swipe it. Be CAREFUL though as it is delicate. You can also get a can of compressed air and blow GENTLY at the lens. Good luck.

thanks Nozz & Timrhu...I'm going to find the part & do it myself. Is it easy to replace the tray with your existing one so the drawer end matches the faceplate or am I way off here? Without taking it apart I can't tell. Thankfully the player still works with some effort reloading discs.

I've used this type: (http://www.amazon.com/Allsop-ProLens-Cleaner-Players-23321/dp/B00000J1QM/ref=pd_sim_23_3?ie=UTF8&refRID=1VJ6KVWZXS0CRXP5RZSF) and this liquid with both a Q-Tip & the included disc: (http://www.amazon.com/DISCWASHER-LASER-LENS-CLEANERS-2-BRUSH/dp/B00I21X5A6/ref=sr_1_1?s=electronics&ie=UTF8&qid=1437755281&sr=1-1&keywords=discwasher+cd+lens+liquid) All have worked for me. I've had a couple transports(someone else's) that wouldn't read a disc enough to use the cleaning disc, and resorted to the Q-Tip/alcohol method too.

I haven't removed the end piece from my Opus 21 but did take off the piece from the drive that came out of the dvd player. I don't really remember how difficult it was but the drive is intact so it must've been fairly smooth.
The Apex AD-3201 is the model that uses the DSL-710A drive.

Go for it.