Bolens's RULE!! They are some of the strongest built tractors made (up until MTD bought them out) now they are just junk like all the other MTD's. I have a few 60's tube frame tractors and they are tanks. They weigh about 600lbs each. The ST series was like a 2nd Generation Bolens. They had to keep up with the market so they made a girly tractor instead of the 3speed ugly looking tube framers. My grandpa has an ST120 but i dont think it is hydro. It is in pieces because he cant really work on it.
Do a search for Bolens, you will find some stuff.
How much did you pay? What condition is it in?