Peter,
The biggest problem is that you are taking a chance every time you boot the CP/M Computer, of having a Floppy drag just enough to partially remove some of the Oxide, and making the Floppy totally useless. Those old 8" Floppys are drying out, and the internal lubrication is probably non-existent. I did this very thing on three of my 5 1/4" Ampro Floppys, a needless mistake on my part.
REF: WARNING - UNAPPROVED METHOD:
http://ubuntuforums.org/showthread.php?t=1569510&highlight=catweasel
I don't know what CP/M System you have, since you didn't specify the name etc, but I'd recommend that you make an Interface Cable for your 8" Drive, and connect it to an older DOS machine, and read the 8" Floppys direct. Not only will that give you a good BACKUP System Disk, but it will take much less time than trying to transfer all the files over an RS-232 connection. (If you must use RS-232 then I'd look for Modem9xx, Modem7, Mex, Mite, or other readily available Software, that hopefully support your RS-232C Hardware, saving you countless hours writing a Driver for your hardware.)
Dave Dunfield has a good article on making such an interface adapter at:
http://www.classiccmp.org/dunfield/img54306/cnct.htm
The problem with the 8" Drives is that they require 24 Volts, a voltage that the 5 1/4" and 3 1/2" Drives didn't use.
22Disk, Uniform, Teledisk, ImageDisk, Xenocopy, and Config on the TRS-80 Model 4 are good software programs to copy from varying formats to a destination format. I've used all of these with the exception of ImageDisk.
Another option is to purchase a Catweasel Card and use the utilities written by Tim Mann to image the complete floppy. His software is written to run on Linux, and I used it on Ubuntu 8.04 for several dozen Floppys. I haven't use it on the later Kernels, so that might be a problem. (I'm planning a test in mid April on a later Kernel.)
http://www.icomp.de/home/indexe.htm
http://amigakit.leamancomputing.com/catalog/product_info.php?products_id=842
http://www.tim-mann.org/catweasel.html
http://www.soundtracker.org/raw/cwfloppy/index.html
Can you answer these questions?
1. What is the Computer System Name? By knowing the complete name and model
I can look in the 22Disk Floppy Definitions to see if your system is supported. (I have several Euro Definition files for 22Disk that are not in my Registered USA Version.)
2. What is the Model Number of the Computer?
3. Do you have some Spare 8" Floppys? For a Immediate System Disk Backup?
4. Are you planning on continued use of the CP/M System, or copying floppys for use on an Emulator? If you plan on continued use of the CP/M System your time might be better spent on purchase of a USB Drive Emulator for your CP/M System from HxC.
http://torlus.com/floppy/
http://torlus.com/floppy/forum/index.php
http://www.youtube.com/watch?v=bHx14xLwY78
You have several options.
Let us know if we can be of more help.
Thanks.
Larry