I recently acquired old steel mountain bike, Specialized Stumpjumper, I was told from early 90's. Absolutely love this bike; already went on trails and it is my daily rider to work and errands. I already replaced chain and cassette, and noticed that fork compresses completely when I ride, there is very little resistance. I suspect it was never serviced all these years. I know nothing about suspension forks, other than what I read on the web. I am wondering it the fork can be overhauled. I posted picture of it. If you know a lik to a site with to DIY instructions, I would very much appreciate. I could not find any useful info. If it is not serviceable, what specs do I need to know for replacement fork? I am pretty sure it is threaded fork. Thank you!