Repair for vintage floppy, Zip and optical drives?

I refurbish vintage systems (mostly Win98/2K/XP), usually for industrial customers whose drive needs are simple. I thought I'd post in case anyone with experience with these older drivers might be able to help me out.

Floppy drives:
I have a handful that seem to function but don't read disks. Is there a 'usual' fix that can be done?

Zip drives:
I've never been asked for a working drive but many of the systems come with one pre-installed. I have no use for them. Does anyone refurbish these (or know someone who does)?

Optical drives:
Most of these customers need a simple read-only CD drive. I have a couple dozen that either aren't recognized in BIOS or won't read a disc. In most cases, I've tried troubleshooting by trying each of them in multiple machines and with multiple discs. Are there fixes I can try for either - or both - of these issues?

Once upon a time, there were "head" cleaning kits for all three drive types.

Have you tried Youtube? I just found a repair demo for my 32-year-old stereo system.
It doesn't pay to repair floppy drives and CD drives. I'll bet there's someone on Ebay or some used parts site selling functional ones for a pittance.

Oops, this is a month old.