I'm going to look at a 1998 Mori SL-300. Any particular issue to look for on this machine?
Good solid machine. Do the normal checks, set backlash comp (parameter 1851) to 0 and check physical backlash. Check for spindle noise,axis noise, hydraulic unit noise, etc. Might want to check turret alignment and if you can chuck up a piece of stock and cut the OD to make sure the spindle is straight. That usually will give you an idea how bad the shop abused it. Run the machine in a test program for a minimum of 30 minutes, doesn't need to move much or fast. You are testing for alarms like waylube pressure etc by doing this. Look for lube on the ways at that point, should see lines of oil across the ways where the axis stopped in your test program. Check for contaminates in the way lube tank, hydraulic tank, etc. Any milky color means water got in. Waylube tank shouldn't have a bunch of crap in the bottom of it.
The only real issue I remember on some SL300's was the x axis gibs would need adjustment after a couple years. No belts or anything like that on that machine. Plan on purchasing wipers and do a full PM when you get it.