Engine swap
 

So as I said in the noob thread I bought a 2006 Cooper S for $500 because the former owner did not take care of the motor so it ate itself. The dealer said they would give him that amount for a trade-in. I'm going to replace the motor and was wondering where the best place to source a new used motor is. I'm going to try for something in the 40,000 to 50,000 mile range. This is not going to be a daily driver as I already have four cars and a motorcycle at my disposal.

What should I be wary of when looking at the "new" motor? I am very adept mechanically and have all of the proper tools except for a lift, so I will have to crane it out and in.

Thanks for any input.