I had a Gleaner K for a couple of years. I used it to do oats and it did a great job. I sold it to a local dairy farmer who found a three row corn head for it. He was using it to combine high moister corn for his cows. He now is a BTO with hundereds of acres of corn and beans and runs several machines. He told me that he sold the old gleaner K last fall and it is still going strong.
I now run a John Deere 6620 and it is way different than that old K. I can only tell you to look any machine over very carefully before buying it. Have someone who knows combines go with you to look it over. Look for signs of rust on the bottom of the machine. They can be patched but most combines do not have a stout frame and are like a unibody on a car.
If you like a gleaner and have a dealer close by then I would say "go for it."