I've got the same problem. I had 2 male degus (Crash and Lightning) but sadly, one of them passed away 2 days ago due to a possible stroke. The one left (crash) is 3 years old. Crash and Lightning didn't get along in their cage since they where 6 months old and so i had to split them up, but they saw each other frequently out side of the cage. I feel that crash will still miss his brother and so needs a new degu friend. What is the best thing to do? I am thinking about getting a new ,male pup because i have heard that pups are easier to introduce. Also, i don't want Crash to go through any unneccesary operations. Any ideas on what to do?