Have just bought an 88 GL1500 (will be collecting it a week today). These are fitted with a casstte player as that was the technology of the day. Has anyone done an upgrade to CD? I see, from browsing fleabay, there is an MP3 upgrade for the GL1800, would this fit the 1500? I'm not up to date with bluetooth but may have to learn if I have to go that way. Any suggestions so as i can start learning in advance?