I went through the IBM servers from PC to PS/2 and xSeries with a few System 36, i and p as well.
Still fixing them, at least for a short while longer.
You should be able to replace it according to this info:
The DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287
Drop-In Replacement for IBM AT Computer Clock/Calendarhttps://www.maximintegrated.com/en/prod ... 2887A.html
Around $22 plus local freight.https://nz.rs-online.com/web/p/real-tim ... s/1898609/
I use RS for most of my parts and find the service excellent.