Difficulty Shifting Gears on Manual (Ford Ranger 2001)

The thing is, the clutch fluid reservoir is at a slight angle (maybe an off-set of 15 degrees from 90), so the fluid looks like it meets one side of the step but it doesn’t touch at all on the the side that’s furthest from the ground. I moved the reservoir a little so that I could get it perpendicular and checked the clutch fluid reservoir; it’s below the step by about 1/4" to 3/8", so it’s not low, to me at least. Is it still worth topping off with DOT-3 brake fluid, even though it’s going to sit at an angle when I’m done topping off? Also, I noticed it was pretty dark, so should I do a complete clutch fluid change? I’ve read elsewhere that it’s a good idea to do so if it’s dark.

Also, I’ve tried driving it a couple times for the past 2 weeks and noticed that it’s not as bad as before, but it’s still noticeable. Double-clutching does relieve it of all resistance, but I’m not sure how much longer I can get away with this? Any suggestions?