Brake light staying on

Hi!

I'm having a problem with my brake light staying on due to the front brake lever not returning to its original position. I've removed and cleaned the front brake light switch and that seems to be working fine. 

So it's the master cylinder right?? 

I have another problem that I can't solve until payday and that's that the screw on the brake fluid reservoir has rounded. The fluid is low and I was wondering if this could stop the cylinder from pushing the lever back into position?

Is this likely or am I going to need to strip the master cylinder etc?

Thanks for any help you can give and sorry if this turns out to be a really stupid question!

There's a spring behind the pushrod that engages the brake lever, it's behind the rubber bung that pushes into the master cylinder. The last two coils snap off due to rusting. It's purpose is to take out the slack in the brake lever. No 23 at this site.
Nothing to do with the fluid level

When you fit the new spring smother it in red rubber grease which will hopefully keep the wet off it, you may also need to replace the rubber boot, no 4 on the same site.

Thats excellent thanks!

Just gotta wait for a sunny day so I can feel me fingers to do the work!!