There are a small number of 08 and 09 Wranglers that have a problem with oil consumption. There are also some that complain that having an Unlimited with a 3.8 and an automatic transmission with a 3.21 axle ratio is light on performance. Since you're talking about a Rubicon it has a 4.10 axle ratio which is good to have with a 3.8. If it has a manual trans. there might be less of a complaint. If you can afford a newer JK with a 3.6 it will perform better. However, certain 3.6 engines in 2012 have defective cylinder heads as an issue. I have a 2 dr.10 Rubicon (3.8) that has as standard a 4.10, like the 08 Rubicon, with a manual trans. and I don't have any complaints. Drive an older JK and then a 12 plus and decide for yourself. If your budget only allows for an older JK with a 3.8 the only way you're going to be able to answer your question is to drive it and decide. A service history of the vehicle would be very important.