4589 = not that I remember/doesn't seem to compute.

4529 = maybe.

But....Struck out.
The 1989 catalog skips from P4529180 to P4529200.

(I also checked a couple engineering cheat sheets, and no luck with either p4589 or p4529)

That's not to say the number never existed. Just that it was never cataloged that I can find.

It wouldn't hurt to try 1990 and 1991 but I don't have them.

My next oldest one is 1998, and all I could find was P4529187 which is an oil filter/no help.

Neither '89 or '98 have P4589 so I just have to assume it's supposed to be P4529, but you can never tell.

I'm at the end of my rope....sorry.

Could be a development part that never was sold to the public. There are a lot of things like that out there.