bring a white paper towel with you when you leave for work, when you park it at work, check the fluid, on flat level ground, wipe the stick off on the towel after looking at the level check the color on the towel.

give the fluid a sniff to, if its dark it will smell like its burnt. your fluid should be a nice pinkish red.

being your at 120,000, id bet the trans has never been serviced. every 60,000 is a good mark.