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You can order a book called; "The Gun Digest Book of Firearms Assembly/Disassembly Part 1, revised edition" by J.B. Wood.
It has an excellent complete procedure for the P-85. The P-89 isn't much different, and this book can get you through most of it easily enough.
Also, in your owners manuel there is a complete parts diagram in the back. It can help you in parts locations.
Now, I have a Ruger Armorers manuel that has plenty of details,,, but I can't get to it right now. It's in a file cabinet that my wife has stacked a bunch of stuff in front of until friday.
Email me directly, and after friday, I'll get into mine, and if you are interested, I can copy the section on the P-89. We'll talk about this.