I just learned this the hard (expensive) way and hopefully this can help out anyone else that runs into this so you can avoid my mistake.
I recently had one of the caps break (for the thire time in two months) on my top push rod AND it got pinched somehow and bent the rod pretty bad. Because I never break anything half way, It bent up the copper bushing and destroyed the rubber grommet that surrounds it.
All easily replaceable except I could not find the bushing anywhere. I eventually found one on ebay and ordered it. What showed up is the correct part I need. But the part number is 999-924-039-00 which is listed as clutch busing for a 944 and 968.
That part you can get easily and cheaply from a variety of sources.
So if you ever need a new bushing for the top push rod, that's the part number. Hopefully you never need one because if you do, you have a lot of work ahead of you to untangle your top and get it working again.