Okay, so posted this on Applefritter, but sadly came to no resolution. What follows is a summary:

Machine: Apple IIc Plus, in excellent condition - very clean and no noticeable corrosion on board or ports, no RAM expansion card

Mouse: Tried two of them:

1. A2M4015 (initally sent it back to seller, thinking it didn't work, but he tested it on his own machine - likely another Apple - and informed me it did work)

2. Super Mouse, purchased through here.

Both mice demonstrated the exact same issue: The cursor on the screen would move in any direction but left, and moving the mouse to the left caused the cursor to move to the right.

So I did some research to determine if this was an Apple IIc/IIc Plus issue, and I uncovered the following:

Link:

I have a //c mouse that doesn't work >> on my //c, but my IIe mouse does. Both work on the IIe and Mac Plus.

>> Whether it matters or not I don't know, but if you look at the model

>> number of the mouse some start with "A2" and some with "M" --

>> presumably this would indicate Apple 2 or Macintosh. I've always

>> suspected the problem (in my case) is with the mouse port on the //c...

>> since it doubles as the game port maybe there's bug.

>

> Possibly ones with an A2 number will work but I also

> was under the distinct impression that since the IIc's

> game port doubles as a mouse port that the mouses

> were wired differently. All I know for sure is that all

> the M0100 mouses I have don't work and all the ones

> marked IIe don't work and all the ones with IIc on the

> label do work. So, IMHO, if you get one that is marked

> IIc you run a better risk of it working. I also read about

> a hack where you add a resistor or diode, can't remember

> which now to the IIc motherboard and it allows either

> one to work. There is also a paddle thing you can do, but

> I'm not so sure I would mess with that. ;-) I now have 2

> IIc mouses that work, and 3 IIc's so I'm looking for one

> more. Very little I need now but much more WANTS.

Click to expand...

Then I found this in the Apple archives:

You have come across an incompatibility in mouse timing. The mouse sold for the Apple IIc works properly, and mice received from service work properly. However, mice that came from Macintosh Plus systems sometimes work and sometimes not, depending on the manufacturer.
To assure proper operation, make sure you use a mouse that was designed for use with the IIc.

Click to expand...

So, there are but two possibilities left:

1. I've an incredible run of bad luck with mice, and a mouse designed specifically for the Apple IIc or IIc Plus would work.

2. There's an issue with the Apple IIc Plus motherboard or mouse/joystick port.

I tend to lean toward Number 2, because the joystick I have doesn't seem to work on the computer either - though I've no way to test it.

So .... does anyone out there have an Apple IIc or IIc Plus, and if so do you use a mouse with it - and if so, what kind? Really, I'm open to any suggestions at this point, including the modification mentioned above.