Service grades have less throat and muzzle wear than the rack grades. The rule of thought is that if the barrels are fresher, then the rest of the rifle must also be as well, but this is not the case in regards to the parkerizing, the stock,and even the condition of the bore it's self.
Having said that, the sevice grade rifles tend to have fresher parts, and for the most part, cleaner bore barrels, but the wood and the condition of the parkering is a total crap shot (read most of the service rifles seem to be armory rebuilds).
As for repairing, on all the models, they will function as is. If you have a problem with the rifle running, CMP will correct the problem for free.
Now to sum it all up since I did do a bit of tap dancing, the best bet is to go with a service grade rifle, buy a new replacement stock, and just have the rifle reparkerized by Warbird if your are going to use the rifle as a shooter and not a collector item. If you plan it this way, then if the rifle shows up with good wood or clean parkerizing, then it's a bonus.