Front Fork External Springs/No Maintenance?
 

I have a 2013 Trek 820 that I use around town. Over the years, the front suspension fork has seized up and it's completely stiff. I looked up videos about re-greasing forks, and it looks rather complicated. Plus one application does not last and my fork will probably seize up once again. I'm now looking for a zero-maintenance fork that keeps on working with very little risk of locking up. Is there such a design or any fork with external springs, or something without a traditional large sliding tube housing that will trap moisture and dirt?

External spring forks look like this : https://www.bikeberry.com/media/cata...m/img_2956.jpg

Trek 820 will probably have a Suntour fork, these are disposable, you can't get many/any spares, and even if you can source them, it will be cheaper to replace the complete fork.

The possibly only maintenance forks currently available like the Lauf fork (and linkage designs like it), which cost 2-3 times the original cost of the Trek, the cheapest option would be to replace with a rigid fork.

Would it be a good idea to buy a used RockShox fork on eBay?

As far as fork "travel" goes the only maintenance free design also has no travel. As in a rigid one. Andy

Buying any used fork, no matter where it is from is taking a risk, you don't know how it has been used/abused, for a lot of lower end forks, the cost of repair/service is similar to just buying a new fork, so you may just be buying a fork which will need service straight away, another issue will be corrosion/stanchion damage, both can effectively scrap a fork.

Unless you know exactly what you are looking for, would consider buying new the best option for forks, even just replacing with a new set of Suntours will get you back on the road.

AFAIK, there's no such thing as a zero maintenance suspension fork . You'd be better off going to rigid. If you do, keep in mind that a suspension forked bike has different geometry than one that came with a rigid so make sure you get your measurements right for a rigid fork. Same goes with buying a replacement suspension fork, make sure you get the correct size.

Riding a big tire mountain bike "around town", the last thing I'd want to lug is a suspension fork. A rigid fork will be a true upgrade.