Whats the problem, 2001 vw jetta has trouble ingaging in reverse gear

The car runs great, all the other gears and shifting is just fine. when the car is started and we try to back up it don't always get reverse gear, we have to shift back to park and try again sometimes several times. My daughter said it seems to be getting worse. the car has 83,000 miles on it and by the way is there a transmission dipstick I looked all over and the car didn't have an owners manual when I bought it (bought it used).