I am in process of buying K9 circa 1996.  Any issues with the early guns.

The early blued guns were known to rust unless taken good care of.
I don't know about the newer guns, but my early stainless K9 has a stainless slide and frame, but almost everything else is carbon steel hard chrome plated to look like stainless.

Some early K9's had problems with breaking the trigger spring.  
This is cured by getting a new design trigger, trigger spring, and plastic trigger "washer".  Note that the "new design" is NOT the current Elite trigger, although you can buy an Elite trigger if you want.  The "new design" trigger parts are still used in the NYPD trigger version of the K9.

Since you'll probably have no idea of how many rounds have been through it, buy a new FACTORY weight recoil spring and replace the old one.
Inspect the plastic magazine followers for cracks or excess wear.

Unless you have good gunsmithing skills, let Kahr install the trigger unit if you buy either the new design or Elite trigger.
Disassembly isn't too bad, reassembly can be very difficult.

IIRC the very early guns had extremely tight chambers, which were somewhat opened up in the later guns.  (I wouldn't bet my next paycheck on that info, but I do recall reading it somewhere besides the internet.)

My wife's early K9––a nickel version––runs like a top as long as I don't reload brass that's been fired through a Glock.

I had a K9 (serial number less than 1000) that I bought in 1993, nickle finish.
A good friend of mine finally convinced me to sell it to him three years ago.

I had somewhere around 45k rounds through it. Was a great pistol, the nickle wore off, and I had it stripped, parked, and duracoated.