After 6 years of faultless and very regular use, My CD50 recently started doing the same - i.e. refusing to stay closed. I fiddled around and tried to lubricate various bits, but to no avail.
So I sold it on Ebay and got a CD5500 (again off Ebay). I feel the difference in price was probably about the same as the cost of fixing the CD50, but with the benefit of a funkier tray and all of the items matching up to read "5500". Oh, and more importantly it's noticeably a better player. 😎
I just need a new MMC cartridge now, which has just lost its mid-range for some reason. Why do these things all wear out at the same time?!