Been a while since I posted here, but I got me a Famicom Disk System!

It also came with the box! (Not pictured)
Got 5 games with it (pictured right) and it works perfectly with three of them:
Super Mario Bros. 2
Exciting Basket
Famicom Grand Prix
Two of them are giving me problems though...
Moero Twinbee (Boots up and plays fine until it tries to load stage 3, then it error 27's)
Zelda 2 (Doesn't load at all. Error 27's at the boot screen.)
The person I got the system from says he just replaced the belt. So no idea if it's the disk system or the disks themselves. I'm tempted to just buy an extra copy of each to be sure before I risk mangling this thing trying to fix it. Any suggestions?