Is this a bushing? Or is it something that is used for packaging the cylinder which should not be installed during use? If it is a bushing, are replacements available?

 

It's supposed to remain in place.

Assuming I had some lying around, would I try a piece of delrin and whittle it with a dremel? Yeah.

If I didn't, I'd buy a $30 slave cylinder and consider it money well spent vs. my time.

 

It's supposed to stay in place, but the consequences of it falling out are minimal.

I'd bet that something well above 90% of all cars that came with that in them have long since lost them.

Looks mostly like a pre-assembly "keep it from falling apart" deal to me.

I wouldn't lose too much sleep over it. The built-in self-adjustment range of the cyl will EEEEEZYLI take up the slack.

 

Like others have said, it won't make much of a difference if its there or not, if you want you could add some grease to the ball end. When new it's used to hold the rod compressed tell its installed in the tranny and when you push in the clutch the straps snap and the rod goes into place.