I'd kep it!..

You'll likely regret getting rid of it,(like some of the others who responded that had one!)..you'll need to find a tube frame Bolens,or an Ingersoll,old Case,or Simplicity/Jacobsen shaft driven tractor to replace it with,if you dont want to feel you cheated yourself..and good luck finding one for less than 500 bucks,and if you do it'll likely be in tough shape..
If I had a MTD 990 with shaft drive and hydraulic drive & lift,I'd hang onto it..
but if your willing to trade it for two Sears "Customs" I'd be glad to swap with ya!..