2000 Subaru Outback--transmission problems?

The odometer reading is 120123. The invoice also lists that they inspected and topped off all fluids. The oil is changed every 3000 miles, give or take a few hundred.

I have no idea when the spark plugs were last replaced or any of the other questions. I can see I’m in over my head in this forum; I’d rather take my chances with the mechanic. Thanks for replying.