Leaky Spool valve

[BCK]

The Bush Hog 1845QT loader on my B2150 has a leaky spool valve in its joystick control valve . It's just a slow drip, but it's annoying because it drips on the step plate, making it rather slippery. I'm assuming an "O" ring is bad. Are the valves difficult to rebuild? Is a special "O" ring required, or can I pick one up at an auto parts store?

Thanks