If it's full of oil, I have no idea how to fix it. Try adding a little oil when it's in the air and see if it goes higher.
If you watch HF, you can get a nice 3 tons for $69, perhaps cheaper. I bought 2 from there. Only had them for 6 months, no problems.
It's sad to say that finding parts to fix some things if next to impossible. It's also sad to say we live in a throw away society. We don't fix computers, TV's, cell phones, printers, and the list goes on. It's cheaper to pitch them and buy new.