Their policy towards replacing these seems all over the place - from 1-1 swaps to the credit mentioned above. I was told two different things by two different people and Springfield - the person in the repairs dept was only going to give me the credit since I bought mine used. I did not have my receipt, so they were going to charge me the difference in retail prices between the two. She was then out for quite some time and I then started dealing with the CS manager. I mentioned that I heard of others getting relacement M1A's at no charge after I agreed to the deal with the repairs folks and she indicated that was all she ever heard was taking place (replacement). She said she'd work out the replacement for me, no charge, and also upgraded me to the walnut stock ;). Couple of weeks later, it finally shipped, but they still charged me. I spoke to the person in repairs who was a bit pissy at this point - she seemed to feel that I "went behind her back" to renegotiate another deal, but it wasn't my fault that she never responded to my multiple voicemails over a period of weeks... Anyway, took a bit of arguing, but I got them to refund the charge.
So... moral of the story is, if you bought it used, there seems to be a bit of room for negotiation. If new, they should do a direct replacement. They will ask for a receipt if used, but I don't think they can reasonably expect you to have it (if you got a good deal on it, you may not want to give them the receipt ;) - claim it was a private sale or something. Make the argument that it shouldn't matter which # owner you were - it really doesn't make sense that they would give the original owner a complete replacement and you less for a rifle in the same condition...
I think you will end up getting a better deal by NOT mentioning replacement yourself. Don't make it seem like you are trying to take advantage of them, but rather that you bought the rifle in good faith and sent it in for warranty repairs in good faith. If you start off asking for a replacement right away, they will likely give you the minimum - apparently there are folks who are intentially buying beater SAR-8's with known issues for this purpose, or in some cases intentionally damaging their own. They know this is happening and I would imagine not very happy about it or inclined to go the extra mile for folks they may suspect of doing this. I found out they were doing this before the notified me, but after I sent mine in - I did not do it expecting a replacement, but rather a repair.
Rocko