Hi Joe,
I have a Miller Cutmate 375. The consumables that I replace the most are the electrode and the front tip.
The torch on mine is an ICE27c, slightly different then yours which should be an ICE12c. There is a metal/fiber collar that holds the tip in. Turn it counterclock-wise to take it off. Inside you'll see three things. The tip (has a hole in it, and looks like a small thimble, and sticks through the collar... The electrode (small rod with wider base) , ... and a swirl ring (phenolic plastic, probably a brown color ring).
I have had my plasma for 5 years, use it alot, and have only replaced the electrode 5 or 6 times, and the tip about the same. I have never replaced the swirl ring, or the outside locking collar.
I'm sure each person's use will vary, and make giving you a straighht answer difficult. However, you will notice a distinct performance decrease when the electrode is worn, and the tip's hole will start to get larger in diameter.
Buy your consumables in a kit. It's a much better deal. Here's a link to the kit that should fit yours:
http://store.cyberweld.com/plcokitsp122.html
Call me if you need more info, or post back here.
Hope everything is going well on your project ... from what I can see in the pics, and what I saw when I saw the car in person a few years ago, ... the project and , both your & Jeff's skills, have come a long way :thumbsup:.