I won't be of much help to you, but I'll just mention what I've seen on this and the SOITC forums.
First of all, I'd avoid the years (2012-2013?) where they used the Schwinteck (sp?) slide system on the bedroom slides. Those have seemed to have been a major problem.
We have a 2010 Mobile Suites and have been very pleased with our 38TKSB3. I have had no real problems with the coach itself, although we did have to replace the Dometic 1350 (I think) refrigerator. It lasted about 2 years and we decided that we would upgrade with a residential, since we already had an inverter and it would give us a lot more space.
If you are definitely considering used, check out Rolling Retreats and visit with Alicia and Slade. They started out with buying used at auctions and cleaning and checking all the systems for resale. Now, they are one of the top selling dealers in the nation as a new sales dealership. Last I looked, they had a fair list of used units "coming soon."
http://rollingretreats.com/
They are also very fine people to work with, because they know the value and importance of customer service.
Terry