Let's talk a bit about maintenance.

Suspension forks have oil and grease and o-rings, so they do benefit from maintenance. If they go too long without it, they will break down the lubricants and lose some performance. There are recommended service intervals that will keep you well under that threshold. I suppose some people follow them. Eventually they will wear out their seals and lose grease and start to scratch themselves up. Definitely don't let them go that long, and if it's been sitting a few years, don't start it up without doing some work first.

Suntour forks of the type we are dealing with here don't have an oil bath, except in the sealed cartridge. All you really need to do is clean the old grease out and smear new grease in. If the wipers (part 2c in the post #6 diagram) are frayed, you can swap them. If the slider bushings (2b) wear out and the fork gets play, you can replace those too. Both of those come in the rebuild kit, which also has grease, replacement locknuts, and the little plastic wrench for the top caps. If you have a cartridge damper that leaks, you replace the cartridge. All the parts are available direct from Suntour US. I can't find a service guide like Rockshox provides, but they have a bunch of videos and each model has an exploded view. If you're just cleaning it out they sell the little wrench for three bucks, but I found a 12 point socket in my tools that fit close enough.

Forks like Rockshox with air springs and oil dampers rely on their air and oil seals so they benefit more from maintenance and stop working correctly if they leak. Maintenance is easy. No, really! You do need to take it off the bike, but that's only undoing some small bolts, as one post earlier. It's easier than a few other normal bike operations that require knuckle busting torques (like crank pullers or cassettes). The rebuild kit is just a bag full of o-rings, and the wipers. The rebuild is taking it apart, cleaning it, replacing the o-rings, and putting it back together with fresh oil and grease. It might seem intimidating at first because when you look at the service manual for the Judy (for instance) you will see that it runs to 89 pages. However a second glance will show they have made a manual for twelve different fork model combinations, given you plenty of pictures for each step, and added a lot of lawyerly gloves-and-goggles stuff. You do need a few tools and goops to do it yourself. The Judy needs grease and two weights of oil, one for the lower leg bath and one for the damper bath. Mostly it uses mechanic tools, but there might be a few you don't have. You definitely need snap ring pliers. In some cases you can make do with a compromise. No manual will ever tell you to use a crescent wrench but you probably have one, and you probably do not have a 24mm socket (unless you are already the kind of person who does everything yourself on your car). Same goes for the torque wrench. It's important to get the oil level right. The lowers need hardly any, barely more than a teaspoon. The manual shows a syringe to measure it. The damper oil is around four ounces but must be measured out precisely since too little will have the compression damper sucking air and too much will cause hydrolock. The manual shows a graduated cylinder but a big baster syringe could work too.