Ila,
I'm in Springfield, IL. Just a bit too far for a visit.
The tension spring is not under any major pressure, but the tiny little screws can be very tight. One thing to do is get a magnifying hood so you can see better what you're doing. Then put the case and tools inside a large zip lock bag and take it apart in there.
The reason to remove the tension spring is that link, thread bits, dirt, rust and what not can accumulate under there and that will mess up the tension.
I get my Evapo-Rust at O'Reilys auto parts store. But you don't have to have that. You might be able to clean the case with steel wool and sewing machine oil.
Then again, it just might work fine the way it is. I always try new (used) parts before I do anything to them just because.
Joe