I guess you always depends on the mbr for booting because during boot the bios brings the first sector to memory and jumps to the code existing on it. If you have there the dos boot sector, it will search for the active partition and then boot it. Lilo and Grub replaces this sector with its own code. So if you have a bad sector 0 your disk may be unbootable.
As you use slackware, for start up your system, you just need the boot diskette or the cdrom from the installation. In the lilo prompt, as you can see in the message provided by slackware,
In a pinch, you can boot your Linux system with a command like:
Of course, you have to change the disk/partition with yours. Speaking about install/uninstall of grub/lilo, both use the mbr or the first sector of the partition. So, if you install one, you are uninstalling the other. You don't need to remove the package from the system.
You don't have to think yourself stupid. There is no reason to have a separate boot partition in most ot the systems. One of the reasons, is the 1024 cylinder limit for the bios to boot in old systems. This problem was circumvented with the lba mapping for most of the disks until now.
If your cdrom isn't bootable, you can't change it. It's the age of your machine and its bios.
About this "CRC error", etc, you may have cabling problems. I had several in my life. Open your machine, dettach the flat cable, attach it again and give it a try.