Does it have a RROD now?
If you don’t have the receipt then MS will use the manufacture date. If it’s inside a year of the manufacture date then they will repair any warranted defect free of charge. RROD is a special circumstance that they have extended the warranty coverage on. Also the newer the xBox the less likely that it will get a RROD, they have been improving components they use internally.
Now here’s the practical advice. Make sure your buddy has not voided the warranty on this xBox. MS will not fix it if he has attempted any home brew fixes and I’ve even heard of them hassling people who send in boxes that have been tampered with. There are a lot of hoops you have to jump through with regards to downloaded content and xBox live. Most of that will not transfer ownership. Unless you trust your buddy completely or the price he is asking is worth it to you to risk losing your money I would avoid this deal.
You can take the serial number and go to the MS xbox website and see when it was manufactured and view what options are available for it before you buy it from him.