It wasn't a good toilet when it was new, and sure hasn't improved with age. You are facing one of the problems others are facing in trying to match the fad colors that were popular 25 years ago and are no longer in vogue. I realize you would like to match the color of the rest of the fixtures in the bathroom, but that just may not be possible (you didn't mention what color the toilet is) Most manufacturers have a variety of color possibilities, so perhaps you can find one that would at least be complementary. I would suggest that as long as you must replace the old water hog, you get one that is a top performer. Old name brands such as Kohler, are not one the cutting edge of technology today. I would urge you to follow the link to Toto toilets found at the top of this page. A new toilet, while not necessarily inexpensive, is an investment that will last for many years to come. You could spend a great deal of $$ trying to clean the old dog up and still have a poor performer.