I just ressurected a 95 VMC15 a few months back. Mine was filthy as well. Had to replace the CRT, hard drive mother board and for good measure I upgraded all of the cards to -5 (current). I had to use about 6 bottles of simple green and three boxes of shop towels to clean the thing over about a week. I replaced the front plexiglass and way covers too. They were pretty dinged up. Happy to say it holds tolerances like new after getting the rep out to tune and calibrate the servos. When he saw it for the first time he said it looked new, it had aparently been cutting plastic most of it's life. The coolant tank looked unused, and the prev owner had rigged up an air blast to replace the coolant.
The controller update was easy. A simple card cage and card swap. Just make sure to label everything before unhooking and set the jumpers correctly on the xyz and spindle cards. You will also have to re-balance the vector drive. You'll need one of those keypads that plugs into the invertor. All of the jumper settings and instructions for balancing servos, balancing the invertor are on the Fadal website. The same info will come on a CD when you order the kit. I took mine to Kinkos and had them all put into big binders, I find it to be a pain to use PDF files, I like books much better.
Congrats on the mill. wish I had 40 X 20! Keep us up to date on your progress.