You can check the fluid conditions via fill plugs of the tranny, xfercase and diffs in about 10 mins. Just Google images of each so you know right where they are when you crawl under.
The TJ is very capable on many trails without lockers. Even with open diferentials, they can go where many locked up yotas can go.
But lockers are definietly nice is certain situations, but before lockers, I would get a good winch. Also a stock D35 and lockers don't mix very well...axle shafts tend to twist and break. So many will upgrade the rear axle to a d44 or a ford 8.8 if they are going to run a rear locker. Some will upgrade the d35 to a "super d35" which also holds up better to a locker.
Check the frame over carefully for rust cancer. light surface rust is normal, but crusty frame rust can be a nightmare to have to deal with.