The Rix is very simple to rebuild. There are a few youtube videos of some things and pdf's of others. I had never done one before (but I consider myself moderately mechanical). It took me ~ 2 hours to tear it down. I could do it in 45 minutes now. It will take maybe 2-3 hours to get back together, but again, 1st time.
I attached a part list of what I ordered (and the prices at that time). You will need a piston storage tube / tool to get the 3rd stage piston back in. If you search my thread you can see most of my journey with pictures.
You'll give Rix your SN and they'll send you the right parts. You can still get parts, but it's my understanding that if it's not on the shelf it's like a 3 month backorder (but at least you can still get them). Rix was nothing short of amazing to deal with, the people were great. I can't say enough good. I probably have 20 emails back and forth.
My suggestion would be to clean it up and see what you're working with. Get the right grease and checkout the swash plate. It might need replacing it might be able to be flipped (it also might be fine). Look at the bearings and the races. See if there's too much play anywhere. See if you can rotate the compressor by hand (without the belt on) or if it's seized up. You can take the pistons out (ONLY 1st and 2nd, DON'T do the 3rd) by removing the bolts. They slip right out. Look at the piston walls and see if they're in good shape. I would imagine most of the o rings are trash if it's been sitting a long time, but maybe you'll get lucky. If all your hard parts are in good shape then order the rebuild for it. If you get that far and start it and it does build pressure you'll need interstage gauges to see if it's the right pressure (in the manual there is a chart that says what each stage should be in correlation with the other). I added liquid filled gauges to mine with the idea I would remove them but I like them and just leave them on the machine. It's a nice sanity check to see what it's doing. I was able to catch a 3rd stage leaking into the 2nd just by watching the gauges before I ever noticed any symptoms.
It is a very cool piece of engineering. The more you take it apart and see the more you'll appreciate just how dead simple it is. If all your hardware is good and it just needs a rebuild you're looking at ~ $450, maybe more if your 3rd stage is out of whack (I think that's ~ $300). After you're done it's rated at 300 hours which equated to 90,000cf of gas. That's more than I'll ever use in a lifetime! Less than $1000 and you'll have a great machine.