my wife rear axle has rusted thru and leaks fluid and I did some digging and found the last one from a gm dealer. I need to know what axle code it is for part(s) whether it is an "C" code or "K" code. When I ordered it new in Oct 1991 got a 3.42 posti. I can just barely make out the RPO codes in the glove box so what should I be looking for to tell me the difference or what code to tell me what codes rear end is in it. thanks

 

The RPO codes for the various gear options are:
- GU6 - 3.42 gear ratio
- GU5 - 3.23 gear ratio
- GT4 - 3.73 gear ratio
- GT5 - 4.10 gear ratio
- G80 - Positraction, limited slip

You also need to make sure that the axle is the same width, as they are different 2wd vs 4wd vs ZR2. These don't have RPO codes as far as I can tell.
2wd 54.5"
4wd 59"
ZR2 63"

This is a very helpful link that DonL shared a while ago in a different thread:
How to find S10 8.5" rear end - PerformanceTrucks.net Forums

 

this info ia already known, what I am trying to find out the difference between a "c" & "k" for ordering the replacement bearing and seals which show different part #'s